Dual processor server, now I have had problems with stuttering voicemail running on dual processor servers, but this was on the Network Alchemy. I have installed ipoffice voicemail on dual processor and quad, without any problems so far.
You may want to check by installing on another PC to test on.
The problem we had with the dual processor with NA voicemail, we had to run on another PC in the end, I think it mite of been something to do with the way the server was handling the processors.