I'd start out here
Buyer's Guide: Value Systems Summary.
The value gaming is $1045 and the value professional is $1545, don't go near the value SOHO though, that thing's a piece....no upgradability at all might as well buy an eMachines (no offense Anand

I'm sure it's great for the folks it's targetted at).
These systems come complete with a Monitor, and are about a month old, so the price are probably a bit out of date...
I'd replace the ABit KT7 with an MSi K7TPro2A and I'd get a TBird 800 or so over the Duron, I'd put 256MB in either way you slice it....other than that it's a pretty good base for a setup. Maybe exchange the GeForce2MX for a G450 if you're sure he's not going to game becuase the G450 has superior image quality. It will play games alright it's about a TNT2 or a Voodoo3-2000 speed wise...but it's not exactly a screamer (or even a moaner

)
You can make a pretty decent system for $1200 without monitor....
In fact you might even want to check out
Buyer's Guide: High-End Systems Summary.
Without monitor the High-End SOHO is only $1660
Cut out a hard drive (it has 2), slow the CPU down a bit, the MSi K7TPro2A over the ABit KT7 (the MSi is cheaper and a better board), and it has a DVDRom and an expensive CDRW, ditch the DVD or get a cheaper CDRW...you should be able to pull together a pretty good machine for $1200