I wanna train with my friend on sf4 but he has an xbox and I have a ps3. I looked for a ps3 to xbox adapter but had no luck finding one. Any tips on how we can train together on one system?
Dual mods for each stick. I think the HRAP3 are non-common ground so you will have to gut both sticks.
Or just get a PC version of SF4.
PCB of HRAP 3 is Common Ground.

HRAP 3 Dual Mod right here.
http://www.ozhadou.net/forum/viewtopic.php?p=51794
Awesome. So there you go. For the 360 stick you can add in a Cthulhu pcb, and a DPDT switch to switch between consoles. This dual mod is easier. He can train at your house.
If you want to go to his house, you need to hack a 360 pcb. You might need to refer to this.
http://forums.shoryuken.com/showthread.php?t=197388
Even if you find an adapter, I suggest not using it as they are prone to either lag or inputs. Just do what everyone suggests above and dual mod it or pay someone to do it for you.
Thanks for the help everyone, this is exactly what I needed.