Right now, it wont make any difference whether you use 32 or 64 Bit.
As time goes on however, what you will find, is that as developers see the benefits of more RAM, you will find the need to have more and more RAM to actually run the programs and this is where 64Bit will outperform 32... You cannot possibly say that you wont need more RAM, because just look at the past...
It wasnt all that long ago when the averge PC has 512K and then 640K ( And Bill Gates said 640K is more than enough for anybody ) and then we had 1MB and then 2 and then 4,8,16,32 and so on, and then 256MB is an absolute minimum, 512K to run XP with any chance of doing more than notepad so today realistically 1GB for office work, and hell most of us are on 2GB and already Vista isnt even here and there is lots of talk about 4GB!!!!
No, RAM is VITAL, and more so each and every day, and Vista32 will be limited to 4GB while Vista64 can talk towards 128GB!!!
Of course, we then also need the Mobo that will take over 4GB because standard Desktop Motherboards at this time dont actually do anymore do they? - thats one thing that a lot of people who try to pimp the 64Bit version of Vista dont seem to realise... Its a waste of time to mention that and any version other than Retail64.