There is no "best" hardware.
What I recommend is to have a dedicated computer for video work, no resident apps, no Internet connection, no firewall or anti-virus etc.. If your input is compressed (DV, MJPEG etc.), I suggest three hard disks. A big'un kept exclusively for your video work, a boot disk for the OS and utilities and the first partition of the third one exclusively for swap files and the rest for your video applications. For RAM, 512 Mb is min and 1024 Mb is the max you will need.
At this stage, there is no significant advantage to be gained from 64 bit processing, as there is no true 64 bit Windows and won't be for some time and no 64 bit video apps. At the most, you will gain higher speed CPU-RAM transfers, but this is not a real limitation, anyway. If you want max horsepower, a double Xeon config would probably get you there, at a cost. However, it is doubtful whether this would improve rendering speeds significantly, as the software would not take full advantage of it, at the moment. I have MSP 7.3 on an HT machine and the performance difference with HT on or off is not enormous. I tend to think HT is more HYPErthreading!