Believe it or not I would recommend looking at Dell. For %1,000 you can get a very nice computer, and Dell comes with a one year on site warranty. Second year is depot only.

You could always have some one knowledgeable, pick up the parts and put a good system together. Dollar wise you can save a couple $200-$300 for a comparable machine, but you loose the warranty.

Spec wise, I would look for the following:

Intel Core 2 Duo
1 to 2 Gig of memory
250 to 350 GB hard drive
A decent video card nVidia 7600 or above, ATI makes some great cards as well, but I tend to lean towards nVidia in preference.
Any system built around a current nVidia chip set, for Core 2 Duo, will be very fast. nVidia chipsets always perform at the top of the pack in any price category.

Shop with these suggestions in mind, and you will end up with a very nice machine indeed.

Joe

PS. Microsoft will not sell any more copies of Win XP after the end of the year. Vista, while newer, demands more resources from your computer, and so tends to run slower in a head to head comparison to XP. So you might want to purchase this fall and go with XP.