PS2 Guitar Hero 3 guitar with a PS3?

Ok. So I just got an 80gb PS3 for Christmas (YAY!). I know it doesn't play PS2 games, but I have Rock Band 2 for PS3. I am considering buying an adapter for the PS2 controllers since I have 4 of them and don't want to spring $55 a pop for 2 or 3 new Sixaxis controllers. I know my PS2 Rock Band Instruments work since they have USB plugs. My question is will my PS2 Guitar Hero 3 controller work with Rock Band 2 for PS3?

Sorry if that is really confusing! I just would like to know if anybody has an adapter or if they are worth buying before I brave the crowds this weekend trying to find one. Gosh, getting this PS3 worked out is a lot of work! I haven't even set up my PSN account yet. Lol! Thanks for the answers and happy holidays and gaming to everybody.

BTW- It works for Rock Band so in theory it would work with Rock Band 2. That is the logic behind my question. I will shut up now. lol.