Hi,
My brother bought a pc a few months ago and these were some things he thought were important.
1. Some LCD screens have **bad** garining on them. If you buy yours by mail order or any other way you cannot see the screen in working order first, find out what screen they have and make sure those manufacturers do not have problems. (In the end, since he spends long hours in front of the pc he opted for a sony as their screens are some of the best. He is a graphics artist, he needs a good screen.)
2. If your new pc has vista on it have 3Gig of Ram minimum. (Note 32 bit vista cannot access more than 3Gig anyway.)
3. A lot of pcs in europe now have bloatware on them when bought. See if there are any forums for your specific pc where people have said which installed programs can be removed. They can sap your running speed if you keep them there.
4. Most manufacturers do not supply reinstallation disk for vista. The **second** (and I mean second) you get your new pc make your own backup reinstallation disks. You might need 2-4 blank DVDs depending on the bloatware on your pc. (Note: The sony was quite nice in this respect as it led you through this process really well.)
Hope that helps (I better not say what manufacturers had graining problems - lawsuits etc)