Have been trying forever to get ESXi 5.0 working on my system:
- ASUS P6X58D Premium MoBo
- OnBoard Marvell Yukon 88E8056 NIC

Unlike ESXi 4.0 the only snag was with the NIC.
Got it working with the use of this excellent forum!
Here's what I did:

1: Downloaded ESXi 5.0 (obviously)
2: Downloaded ESXi Customizer: http://v-front.blogspot.com/p/esxi-customizer.html
3: Downloaded the appropiate driver from Peetz (epic lifesaver!) in this post: http://www.vm-help.com/forum/viewtopic.php?f=25&t=3558&p=13787#p13787
4: Used tgz2vib5.cmd from the ESXi Customiser to generate an ISO image containing the new drivers.
5: Burned the ISO to CD

Booted, installed, worked like a charm!
One happy camper here