I think I have the answer. I was having almost exactly the same problem. Then I remembered that the power pins on the USB cable touch before the RX TX pins do. It turns out I hadn't inserted the USB cable all the way into the Arduino Uno USB socket. Once I did so, I heard the USB device installation noise and was able to install the drivers as per the instructions. Now I seem to be working fine.
I hope this helps.
Ray
Thanks guys, following all of your advice I played with it on the xp computer last night, it wouldn't work (still) so I left it plugged in and turned off the computer. This morning I turned it back on and the Uno showed up in the uninstalled hardware (don't know why, I tried booting up before with it plugged in). I was VERY careful about which driver I installed, to the point where I actually deleted the FTDI driver folder altogether to make sure I didn't get it wrong. I was having trouble identifying the inf driver, all I found was a notepad type file..........
Right now it is working and I can install programs, (modified blink, yehaa!) on my XP machine, I am very happy, later I will tackle the 7 machine.
I think it was plugged in all the way, but I will be checking that more carefully in the future too
You guys are awesome, many thanks for all your help.
Now I can start to play & learn, should be fun............ 8)
(& hopefully it will keep working, I am a little scared to unplug it from the xp right now! 
Cheers
Dave
Dave
Most hardware leaves the usb port powered up, even during a reboot (unless you set it in bios).
I think we need to include the instruction "remove the power from the computer, inc battery on a laptop" as a hint if you can't get the pc to recognise a new device.
The inf files are a plain text file. Once you get the hang its not too hard to read them.
Heres what I found out during my adventures.
The attachments will help, these are from my computer and yes the UNO is using the Freetronics driver (its the same)
You need to identify the VID_xxYYzz...&PID_xxYYzz... numbers, within the driver .inf you made windows install. (You can also search each usb device)
Open up Regedit (Start Run type in regedit and press enter).
Under EDIT there is a find option, so enter the VID&PID (in this case Vid_2341&Pid_0001) (see Regdit.jpg attachment)
It should be in HKey Local Machine System ControlSet001 Enum USB (Note this sometimes get abbreviated to HKLM \ System \ControlSet001 ..etc)
There is enough english words there to work out this the one you're after.
The Device parameters shows which port it will use.
Copy the ClassGUID (easiest way is double click it, and then copy with Ctrl and C (very useful to remember as its an underlyingwindows function).
Click My computer at the top so that the search starts from the top, and then EDIT find and paste by Ctrl and V. Hit the find next.
It should bring you to HKLM ControlSet001 Control Class (see Regedit2.jpg)and if you open up the entry there a series of numbers which should match the port number. In my case it installs as Port 4.
So you've identified the device, and found out where windows hides its info, but what does it mean.
Well .... InfPath contains an oemxxx.inf, which is a copy of the driver you pointed windows at. (Or it thought it would use)
oemxxx.inf gets loaded into C:\WINNT\inf (or C:\Windows\inf) for XP.
Note this is a system directory and is often hidded. You can force Explorer to go there by typing it at the top.
If you were really keen to make windows ask for a new driver, you can make the oemxxx.inf go away by adding old_ to the front.
NTMP states it uses usbser.sys to talk which is the same in XP and 2K (not sure for the rest).
You can look at this to verify the version. It resides in C:\WINNT\Sytem32\drivers (or C:\Windows\System32\Drivers in XP)
There have been some fixes for the XP version, and in my case I loaded the newer one into Win2k (it didn't even complain).
Hope this helps someone, as i iknow how frustrating it can be, I spent at least 80 hours to sort mine out.
Mark
Hi Mark,
You know what, when I get the chance this weekend (it's Mother's day weekend with all that entails) I will follow this step by step on the windows 7 laptop and will let you know what happens.
Then maybe I can give the kids the XP computer like I was suppossed to before I had to experiment with it! But once I get into the Arduino and understand it then I really want to teach them early so this stuff comes easily to them, I have been looking through the 12 projects in the book and once each one is understood there are all kinds of applications we can play with by combining different parts.
Watch this space for the results of the top paragraph.
Cheers, 
Dave
Understood.
Not sure how Windows7 does it, I haven't progressed to it, as new motherboard, ram and power supply reqd.
i also don't relish the thought of spending a week or more installing the multitude of programs I have on this one.
send me an email m(dot)beckett(at)paradise(dot)net (no nz, you know what to swop but the trolls don't)
I have a number of links for tutorials I can send.
I would get into an LCD quickly, much more feedback than just lights.
The DS1820B temp is also good as its instant feedback.
I also have a simple robot project that would transfer to Arduino easily.
You could also check out Hannos 12blocks. He resides in chch, and its very clever. Works with picaxe, parallex, arduino, basic stamp and some others either as graphical or text. http://12blocks.com/.
He had 6/7 yr olds making thing work in 10mins using it.
Cheers
Mark
