Are you typing the command exactly as shown, including the "sudo" bit? That gives you root permissions so you should be able to move the file.
sudo mv /etc/apt/sources.list /etc/apt/sources.list.backup
Andrew
Thanks Andrew.
Is there a space after "mv" and the first "list" ? If there are spaces then I have typed it in correctly.
The permission denied message only came up after typing the second line:
sudo echo "deb http://www.uk.debian.org/debian stable main contrib non-free" > /etc/apt/sources.list
Ive tried it 3more times and now another message comes up
mv: cannot stat '/etc/apt/sources.list': No such file or directory
after typing the first line when before i was able to type the second line without a message coming up until after the second line.
Im double checking and Im typing it all correct.
Im trying to upload a screenshot of the terminal window in this reply but I cant seem to.
Am I useless or is my machine not cooperating?
Can anyone help me?
ps. Ive just done an F9 restore and updated BIOS but I still get the same message:
mv: cannot stat '/etc/apt/sources.list': No such file or directory
after typing the first line in step one.
Lost.
If you do a
ls /etc/apt
Do you see a "sources.list.backup" file?
If so, the first command has worked and you can move on to the second one, the "sudo echo" command to create a new "sources.list" file.
Andrew
Thanks.
I did the:
ls /etc/apt
and
apt.conf.d/ sources.list.backup trustdb.gpg trusted.gpg"
secring.gpg sources.list.d/ trusted.gpg
Is all OK here?
I type the second line and I get the message as before previous:
bash: /etc/apt/sources.list: Permission denied
Appreciative but confused
Nathan
Ok, the first command has worked, making a backup copy of your sources.list file. Now we need to create a new one with the source of the gcc installation files in it. I've added some extra spaces below to make it clearer where they go - any extra spaces where shown won't hurt anything. There are also spaces after "deb", "debian", "stable", "main" and "contrib". And don't forget the "sudo" at the beginning so the command is run as root.
sudo echo "deb http://www.uk.debian.org/debian stable main contrib non-free" > /etc/apt/sources.list
Andrew
Andrew, thanks for this.
Taking great care to get all the spacing correct I still get the same message as before:
bash: /etc/apt/sources.list: Permission denied
I hope you can help me further.
I cant find anything on the eeeuser.com forum
N
You're typing the sudo at the beginning and it asks you for a password?
Andrew
Yes, Ive written it just as you have with the correct spacings and with Sudo at the start. Ive done it maybe 5 times and each time it gives me this reply:
bash: /etc/apt/sources.list: Permission denied
It doesnt ask for a password, it just gives me the "/home/user>" prompt.
Ive typed in my password just to see, but it gives back:
bash: my password: command not found
Man, I dont have a clue about this linux Xandros stuff, so great you can guide me through.
N
OK, I've dug my eeePC out of storage and think I've got it figured out. Before you do the "sudo echo" command, first type
sudo touch /etc/apt/sources.list
then
sudo chmod ugo+rw /etc/apt/sources.list
and then carry on with the "sudo echo" command as before.
What that does is create a zero length empty file and make it writable by everybody. Once you've gone through the rest of the instructions and moved the original file back into place it will go back to having more restrictive permissions again.
Give that a go and see how you get on.
Andrew
I had the exact same problem as nathanxl and I don't know my way around a command line as it scares me, but I did find out that /etc/apt/sources.list:is owned by root.
I typed the following line to get root access:
sudo bash
There always seems to be little inconsistencies in a lot of instructions that make it very difficult for noobs like me. 
That stopped the "bash: /etc/apt/sources.list: Permission denied" error so I could continue.
WARNING! The first line in step 4 appears to be wrong.
It reads:
sudo mv /etc/apt/sources.list.back /etc/apt/sources.list
where it should read:
sudo mv /etc/apt/sources.list.backup /etc/apt/sources.list
If it is easy for the experts to let typos creep in, imagine what my command lines look like! :-X
I eventually got my Eeepc 701 talking to my Arduino, and now I am a happy camper once again. 
@Macro, yep, that's another way of doing it, get into a root shell and you can do whatever you want. A bit dangerous though as you can do whatever you want...
I've fixed the typo in step 4.
Andrew
OK.
Andrews work around got me to step3 of installing the packages.
after 190 packages and 50mins waiting, a message at the end mentioned that I should do a get update. I did but nothing seemed to happen.
I continued and successfully completed steps 4, 5 and 6.
I can open the IDE fine and the connected Arduino randomly blinks as Im led to believe it should.
I wrote the Blinking LED Sketch from the "getting started with Arduino" book... But I still cant get started. 
The same message that I had at the start comes up when I try to verify the sketch...:
java.io.IOException: avr-gcc: not found
What should I do now?
Macro did you have this problem? You said:
"/etc/apt/sources.list:is owned by root.
I typed the following line to get root access:
sudo bash"
If I get root access will I be able to get rid of the "avr-gcc: not found" message?
I have no idea what root is mind you.
All I want to do is start playing around with Arduino on my Asus eeepc 701.
Shattered.
Did the "sudo apt-get install build-essential avr-libc gcc-avr" command appear to work correctly or did it throw any errors? If it took 50 mins I assume it was downloading lots of stuff.
Andrew
After spending the last 2days trying, F9ing, trying, F9ing and trying again I have my eeepc communicating with my Arduino.
After doing the sudo apt-get update in step 2 an error comes up on the first package, "stable release.gpg"
When the 2nd package has finished, it has fetched 74.9kb in 5seconds and the "reading Package lists is done" an error message comes up in terminal:
W: GPG error: http:www.uk.debian.org stable release: The following signatures couldnt be verified because the public key is not available: NO PUBKEY 9AA38DCD55BE302B NO_PUBKEY 4D270D06F42584E6
W: you may want to run get-update to correct this problem.
I run get update and the same W:GPG error messaage comes up.
I continue on to step 3 anyway and after 50mins watching and downloading 190packets it all seems to go without any errors except that at the end, when confirming yes to an action and clicking through multiple blue screen warnings it uninstalls my OpenOffice suite and god knows what else.
So as it stands I cant open MSword .docs but my Arduino now runs fine.
Thankyou sooo much for your assistance Andrew and Macro, I would have been completely lost without it.
Now I have to search elsewhere on how to get OpenOffice overriding the troubles and installed perminantly.
Cheers
Nathan
This is my very first, so here we go!
I have the Asus eeepc 701SD but cannot install the software.
sudo apt-get install build-essentials ........... asks for Yes, do as I say
and then aborts.
Please help
I have made progress by using sudo bash apt-get install build-etc
Now all I have do is work out how to adjust the screen size.
This entire Xandros thing seems to be a bit fragile to me!
Peter