And let me tell you something.
When you buy a computer, it's for the 5 next years, not for today or the last 5 years.
For sure, all the next versions of software will be 64 bits.
Many 3d software are allready 64 bits: Vue, Cinema4D, Photoshop CS4, 3D Studio Max, etc...

So go for Intel i7 and Windows 7 for the future not the past.

And for another 300.00$, buy 12 gigs of memory unless you have only Poser as software.

Good Luck