buying a new pc?
Personally, no sempron or celeron cpu for me. Athlons or Pentiums/core2 are ok.
Minimum 1 GB RAM. DDR2 667 or 800MHz. Dual channel better.
Get a good mother board, don't stinge on this. Very important! Recommend Asus, Gigabyte or Intel motherboards.
Check out how I chose a system for running Vista.
http://www.janleow.com/life/a-new-year-a-new-pc-%e2%80%93-gigabyte-ga-ma69g-s3h.html
Graphic cards, depends what you want out of your system. If you need budget and low cost, integrated graphic chipset would be good. Playing lots of games or doing heavy graphic editing? Better buy a separate PCI-ex graphic card. NVidia or ATI chipset would be good. Get about at least 256 to 512MB of graphic memory if you can afford it.
Minimum 40GB HDD space, using SATA2. If you have lots of data like MP3, photos, and other loads of media junk, go for 160GB or more. Not much price difference anyway, so may as well go for bigger HDD.
And of course don't forget your DVD-ROM.