Why you won't have to worry about whether or not your computer and its applications are 32- or 64-bit with Mac OS X and why you will with Windows Vista: article.
So why haven't you bought a new Mac? They can run all your "necessary" PC apps in a safe sandbox via Parallels or VMWare (beta).
(Okay, Bert, I know your reason. ;^) Price. But find something comparable before you say it.)
Did I forget to mention that these things are fast? Just as fast as PCs these days. *sigh*
Here's the vivisection of one. Did you work on the drive?
UPDATE: A price comparison between Apple and Dell.