I just added a download tonight:http://code.google.com/p/pg3b/
If you want to run on a non-Windows machine (though this is untested):
java -Djava.library.path=native -jar pg3b.jar
You may need a fully qualified path to the native directory.
It works even if you don't have the PG3B hardware. Eg, click Capture to activate the example config, then left click to play a song.
Of course all the cool RSTA stuff is on the Scripts tab!
I originally bought an Xbox 360 just to play Street Fighter IV, so I chose the cheaper system. Plus the Xbox reportedly had more online players. The PG3B project might still apply to you though! PS3 peripherals work on the PC right? If you got an Xbox, you would be able to use your PS3 peripherals with the Xbox.
The PG3B hardware itself isn't actually tied to Xbox. It may be possible to wire it up to a PS3 controller. However, the other owner on the PG3B project, Rick, is the EE genius, not me. Playing first person shooters with a keyboard and mouse is the only way to go!