Heres the spec of my ESXi4 whitebox
AMD CPU AM2 7750+ Athlon 64 X2 Dual Core
Xilence Quad Core Socket AM2 754 939 940 CPU Cooler
Maxtor 320GB Diamondmax 22 SATA HD
Geil Value DDR2 4GB Kit PC2-6400 memory
Gigabyte motherboard M52L-S3 nForce 520LE
Samsung SATA DVD RW SH-S223F/BEBE
Extra Value 4GB Kit (2x2GB) DDR2
2 x Intel Gigabit PRO/ 1000CT PCIe Desktop Adapter - OEM Version
And an old Maxtor 40GB IDE drive as boot drive
On board LAN adapter doesn't work but I had to keep it enabled otherwise the USB keyboard stoppped working?
Other than that all is good so far, hope to get another NIC at some point and bigger SATA drive.
Originally tried ESX 3.5 but it couldn't see the SATA DVD, after much messing about with IDE DVD/CD drives went with ESXi4 which is working fine.