The 360 rock band ones are USB. I have used both the mic (which is still not the greatest, but works) and the drums(which work flawlessly.)
You can use a wired 360 guitar (I have tested Rock band I stock wired guitar and GH2 wired) and PS2 guitars, but the whammy will not work. To use The PS2 guitar, you will have to either do a bit of wiring to create a usb connection for it, or find an adapter for it, which I think they have on eBay.
If you have guitar hero I or I think II you can extract the songs from the CD, but this is a lengthy process.
There is a frets on fire forum with a list of songs that people have created, but be warned, fretwork is usually not the best on any of these. http://fretsonfire.wikidot.com/custom-songs
Shoot me a PM if you give it a try and there is some stuff I can give you.
Yes, I completed the activation that got emailed to me. On every other Vbulliten forum I can remember, after that step I could post immediately. But this one its telling me I either didnt complete the email activation, or my account was disabled,.