Good idea.
If you do surcumb, get the best one possible. Apparently Vista will not do it's whole thang unless your machine meets certain benchmarks, like a 1.8Gb/second memory access rate!
I think a CoreDuo machine will be safe, and very very fast. Rule of thumb is to always buy the best machine you can afford.
If you are feeling adventurous, I did switch to Mac after PC for many years (though have always loved Macs and had them during uni) and I have never looked back.
I am currently running an XP virtual machine that runs concurrently with Mac OS X so I have the best of all worlds... check out
this video of a mac running Windows, OS X, Linux and Plan 9 all at the same time!
In defence of staying with a PC though, Office is not so great on an Intel Mac because they don't have a native binary for it yet, and so it runs on my new CoreDuo laptop at the speed of my old PowerBook G4
