ESXi 3.5 and 3c905c

I can confirm that ESXi 3.5 can "see" the 3com 3c509c NIC without modifification. You're more likely to run up against issues with the storage controller if you're running 3.5 on newer equipment. However, before you attempt to build a custom install disk, try tweaking the drive settings in the BIOS. I managed to get mine working after changing the RAID settings and reformatting the drives. Others have had luck with turning off AHCI.