Here is a breakdown of what I recently bought to upgrade my computer - I basically started from scratch and the only things that I kept from the old computer were the floppy drive, two optical disc drives, and the hard drive with the operating system on it. And of course the monitor, keyboard, and mouse.
1. Raidmax xB ATX528BP Mid Tower Case (Black) included 330 Watt power supply.
2. Asus M2N4-SLI nForce4 SLI Sempron/Athlon 64(FX)(X2) SktAM2 DDR2 ATX Motherboard w/Audio, Gigabit LAN, RAID/Serial ATA. - X2 is the socket type that the pins on the back of the CPU would fit in. Match these up.
3. Gigabyte GV-NX71G512P8-RH GeForce 7100GS TurboCache 128MB DDR2 PCI-Express Video Card w/ Dual DVI. - (Cheap but works OK).
4. Ultra ULT31876 80mm Sleeve Bearing Case Fan (5 Pack) - I ended up with four extra fans - case didn't have the open slots for fans that it advertised
5. AMD Athlon 64 X2 Dual-Core Processor 3800+ Socket AM2 (65W)
6. Corsair TWIN2X1024-5400C4 1GB Kit DDR2-675 XMS2-5400 Xtreme Performance Memory w/Black Heat Spreader.
I also added a 320 GB hard drive and installed Quake 4 on it - it is faster than my old hard drive but it didn't make Quake 4 run any faster. With this system Quake 4 runs fine on my computer but has to run in medium quality for video (600x800 or something like that) otherwise it bogs the system down. If you have a few extra bucks get a video card with more base memory than the 128mb card I bought. And make sure to get at least 1 gig of memory (see #6 above). I got to the bottom here and realized you only wanted CPU/Motherboard info. Sorry. Hope this helps!