In Europe all you can buy is RB: Band in a Box (which is RB1 instruments), and that will be the case until they clear enough back stock, or you get RB: Beatles edition, which uses cutomized RB2 instruments. GH: WT are pretty much the same as RB2 instruments, but you can buy GH: WT now in Europe.
What I did was got GH: WT bundle, going to buy RB2 that supports GH: WT instruments, then going to rent RB1 so I can put the disc in and unlock all those tracks in RB2 for five quid (something like that). That way I've got all the music, good instruments and at a reasonable price, though I will be buying a madcatz guitar for the bass so I have a full band setup.
Whatever you do though do not buy the RB: Band in a Box set though, there crap as Req. says
P.S I got my GH: WT only last week for the PS3, really like the instruments, even if the drums seem crazy difficult compared to the guitar, even on easy level, so I'll be interested to see RB2 difficulty when I get that