nothing special, all you need to make sure is Windows Vista need at least 4-5 GB Harddrive space in C:\ ... you are fine ...
The rest of the hardware, just get what you need ...
I still recommend a desktop or laptop with brand names, like HP/Dell/IBM/Sony/Toshiba ... etc ...
and stay away of custom-made system, since those are for gamer or expert ...
cannot save you a lot of money :P