This is from our documentaion at Avaya:

Check the following requirements before installing the voicemail software
onto the voicemail server PC. The software is installed from the IP Office
Administrator CD.
PC
The PC used as the voicemail server should have:
• A Windows 98 (2nd Edition), NT4 (SP6), 2000 (SP2) or XP
Professional PC.
• A Pentium 166MHz or higher.
• A 100Mbps network card is strongly recommended.
• It is strongly recommended that the server PC is dedicated to this task
and is located in a non-public area.
• Installation on the same PC as being used for IP Office Manager is
recommended.
• Switch off any PC and hard disk sleep/power down modes.