For $400 you can build a decent machine perfect for using the web, maybe a few applications, and with a decent video card you can play games on it.
I am building a new computer right now as a matter of fact, it's a mini pc meaning it has a very small case to it, which is what I want because I like to LAN.
-Athlon XP 2000+ (I plan on OCing it)
-512MB PC2700 Buffalo tech ram
-40GB WD Hard Drive
-256MB GeForce FX 5200
-LITE-ON 48x24x48x16x Combo Drive (cd burner + dvd-rom)
Here is the bare bone I am starting out with, since it's easier to just get a barebone kit and buy everything else when you're dealing with mini pc's. http://www.newegg.com/app/viewProduc...6&searchdepa=0