Using USBtinyISP programmer

I was inspired by http://www.arduino.cc/en/Hacking/Programmer to try to use my USBtinyISP AVR ICSP for uploading sketches to my AVR. I followed the directions for altering the preferences (changed upload.using=bootloader to upload.using=usbtiny). When I hit the upload icon though, it returns the following message

avrdude: Can't find programmer id "null"

Valid programmers are:
dasa3 = serial port banging, reset=!dtr sck=rts mosi=txd miso=cts [hardware/tools/avr/etc/avrdude.conf:582]
dasa = serial port banging, reset=rts sck=dtr mosi=txd miso=cts [hardware/tools/avr/etc/avrdude.conf:569]
siprog = Lancos SI-Prog http://www.lancos.com/siprogsch.html [hardware/tools/avr/etc/avrdude.conf:556]
ponyser = design ponyprog serial, reset=!txd sck=rts mosi=dtr miso=cts

and so on...

This doesn't make sense to me since I have altered the preferences.txt file. Any help would be appreciated.

On the link page you list there is a notation " Note that when you upgrade Arduino, this folder may not be deleted. If you are having trouble, delete this folder. Upon launching Arduino a new file and preferences.txt will be created. " in the editing the Arduino preferences file section.

Maybe doing this and then changing the pref. might work.

Thank you for the suggestion.
I tried this and it unfortunately didn't help. I am wondering if this is an issue with AVRdude or AVR-GCC interacting with the Arduino environment. I am going to play around with the configuration of AVRdude and hope that that works. If anyone has any more suggestions please let me know though.

Thanks,
Gabe

As it turned out, I needed to use the identifier "usbtinyisp" and not "usbtiny" in preferences.txt . Thanks again for the suggestion though.