Win 7 64 bit is vastly better than vista. 64 bit o/s's ARE the future. XP is a dying beast at this point.
You can install a 32 bit DAW on a 64 bit o/s (I run Cubase 4.5 32 bit on win 7 64. While the 32 bit app cant access all of the ram that the O/S can use, Cubase now get's the full 4 gig of ram that it is capable of accessing (vs the previous 3 or so that I could get it under win xp). The additional ram makes a VERY big difference.
32 bit plugs will also run fine on win 7 64 bit. The bit bridge issues only crop up if you're trying to use 64 bit plugs when you're running a 32 bit DAW (or vice versa). As I said, I run Cubase 4.5, 32 bit and boatloads of 32 bit plugs and VSTi's....Waves, BDF2,
Omnisphere, Kontakt 3 and 4, Easy Drummer, Antares stuff etc.... all under win 7 64. Runs fine.
Be very careful about the interface you select. This is where you have to insure that the interface has a solid 64 bit driver available. I used to have an M-audio Delta 1010. Ran the 64 bit win 7 driver for it. It worked pretty well. They can be found fairly cheap on ebay.
At this point, personally, I'm a believer in RME interfaces. I've tried lots of stuff and their gear has just proven to be so solidly reliable and trouble free that I'll spend the extra money and consider it well spent in avoiding problems and hassles.
BTW....I've run Reaper 32 bit on Win 7 64 bit o/s. Works fine.