Ok here is what i gotta say about this, (sorry if its prementioned)
Pre-Package is just fine for some people, alot of people just point and click web browse, music and movies, and downloading pr0n. and video games, yea that too.
If you get prepackage watch out for Intergrated video, that will leach off your ram, and your game will not run as smooth as you want it to.
Also look out for the ram type, things are going to ddr2 dual channel, make sure the mainboard supports ddr2 dual channel and not just ddr or ddr-dual channel.
But its also getting hard to find a pre built with XP pro on it.
And you might want to do heaver activities on your computer, such as high end graphic projects for school or work, high end video editing (not Windows movie maker)
Lots of applications at the same time, or never wanting to turn your computer off. (mine is only off when i am out of the country)
If you are using same monitor you can have a computer built for same price or cheaper then most prepackage, but the catch is you gotta know what to do. Or know somebody that does.
If you gonna get one built, again look to DDR2 Dual Channel Ram, and SLI-Graphic card support ( allows you to run two video cards as one, works great with recording gameplay )
and meby a power supply that runs 580 watts+
I think you know about the rest, HDD space, Burner and all.
but yea, let us know what u gonna do.