yup, Dak and I have just about upgraded to the same spec.
Different Gfx, I've got hold of an XT800 and Daks using something slightly better, but both are PCIe 16.
The board we've gone for is an ABIT KN8 SLi. not really using the SLi, but the price is low enough not to worry about it.
It takes DDR ram, up to 8Gb. runs PC3200 as well as slightly older stuff.
Most other boards are using DDR2, fine if you've got the cash to do the RAM as well.
Both have gone for AMD64 3200 Venice core (not the AM2), Daks got his clocked up to 2.4 I thionk and it's as stable as a Horsey house.
I've gone for and OEM version with an aftermarket cooler, though i thinks Dak's was retail.
We were thinking of Opterons, but they're quite a bit more expensive.
Both have also gone for a SATA 160 Gb drive as well, Scan have some at a decent price.
Daks as impressed as anything with his new rig, I'm still waiting for my parts and some time to do a rebuild and install.
Mobo, CPU and HD came in at about £160.
Up to you how much you want to spend on Gfx.
If you want to have a quick squint at the thread where we discussed all this over at the Marlins....
<a href="
http://www.ma-squadron.co.uk/forum/view ... sc&start=0" target="_blank">Linky</a>
Fair bit of rambling, but there's some good bits