Mine is also custom/homebuilt, but on a 17 year olds budget
Celeron D (2.8GHz...says 2.66 on the box, but with some tweaks...)
512MB RAM (need more!)
2 Sata HDD (one for / (30GB), the other for /home/civint (120GB))
And a XFX GeForce 6200...which I will be making use of the dual monitor ness which I am informed the 6200 can support, which will be fun!
I am running desktop effects from "desktop effects"...dunno if it's different to using beryl or compiz, but it works like a dream. I did also have xp on my HDDs, but in a install, it screwed up my mint install as well, so I had to do a fresh HDD, which turned out to be a good thing, since it's all now under control.