I've follow this forum tips and got ESXi 4.0 running on this system:
Motherboard JetWay NC81-LF (Mini-ITX, Socket AM2+)
CPU AMD Athlon II x64 600e (quad-core, socket AM3, 45 Watt)
Memory: 4 GB (2 SODIMM DDR2-800, 2 GB each)
ESXi boots from USB (a SDHC adapter with a 4 GB SHDC card)
My first datastore is a 500 GB SATA2 disk, connected to 1 of the 4 motherboard SATA connectors, in AHCI mode. There was no need to use special drivers, ESXi recognised it as soon as I hot-plugged it in).
I only had problems with NICs: motherboard has 2 Realtek RTL8111C onboard (PCI-E) and I only have RTL8169 PCI cards. All not supported but a oem.tgz from this forums (I believe these: http://www.vm-help.com/forum/viewtopic.php?f=12&t=1670
) works with both.
Having some problems with network, sometimes drops connections and never repairs it (even if I wait a all night) until I unplug/replug cable. Things got better after I put 3 card (2xRTL8111C + 1xRTL8169) in the same group.