Alright, I'll list what I have in mine. lol
TDK 52x CD burner
Seagate 60gb barraduca
MSI K7N2 Delta ILSR
AMD Athlon XP 2800+
768mb of RAM
NVIDIA Geforce 3 Ti200 - I reccomend getting the Ti500 or going for the Geforce 4 Ti4200 or Ti4600. The FX 5600 Ultra is the only good card in the FX series right now.
Netgear WG311T wireless NIC - Works with Madwifi drivers which are native Linux drivers. I'm using it right now.
or
Netgear FA311 NIC[wired] - Uses the National Semiconductor chipset which the Linux kernel has drivers built into for. I used to use it and it worked great.
Sound Blaster Live 5.1 - Buying this instead of the Audigy 2(which also works with Linux) will save you quite a bit since it's still a great audio card but it's cheap now adays.
I recommend getting case made by Enermax if possible. Their cases are made of a steel and alluminum alloy which makes them the next best thing after alluminum.
Well, I suppose that's it for now. I hope this helps you make a decision.