I've been running Trainz 2006 and now TS2009 on Vista Ultimate 64-bit since May 2007. No problems at all in fact 2009 runs really nice on the 64-bit platform.
I recommend not chintzing out your RAM or disk space though. The 64-bit OS needs at least 4-gig to operate comfortably and be able to handle applications such as Trainz. With the 4-gig, there's nearly no stutter or pauses when in Driver.
I have no quantitative evidence to support this, but Trainz sure seems to run a lot better when I upgraded from 32- to 64-bit Vista Ultimate. I agree with JCitron: do not skimp on RAM. I'm running TRS2004 and TS2009. Enjoy!
If you've taken a fancy to using one o' them RAILDRIVER control gadgets, you've have to put it back on the shelf to gather dust. 'Taint no support for 64-bit drivers, and it may be awhile.
I am moving to an Alienware M17 notebook with Windows Vista® Home Premium (64-bit Edition); 512MB ATI Mobility Radeon™ HD 3870; 8GB Dual Channel DDR3 SO-DIMM at 1066MHz RAM; with the Intel® Core™2 Extreme X9100 3.06GHz (6MB Cache, 1066MHz FSB).
