To build or not to build

[AMDnewbie2005]

I would like to know whether it's worth building a new rig to play games such as doom 3 halflife2 and f.e.a.r. We have a dual 1.8ghz xeon computer(which is pretty much a workstation) with 512mb of rdram and agp 4x with a geforce fx 5700le 256mb that is not really keeping up with all the new games(but i cant complain because it was free).
If i do build a new computer, I'm on a bit of a budget so I'd like to know if it would be worth going with a socket 939 and an SLI mobo considering how expensive it is
or just a socket 754 with AGP, high performance RAM or valueram which is alot cheaper because I'll probably only do an AI overclock with Asus because I don't want ruin any components trying to do it myself.

 

[McCloudb182]

the 939 set, because it leaves much more room for upgrading in the future, no doubt about it.