Thats a good question. Never tried this ona custom server that still is better than Cisco MCS servers are. Worst case you can install a licensed copy of Win 2k3 and then use the /nopcd switch while running setup.exe from Unity connection setup files.
HTH
Sankar
PS: please remember to rate posts!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus