I installed jive 2.3.0 on a 2003 server with dual 3.4Ghz and 2GB of RAM and it was painfully slow. I have 900 users in AD that I was using in a few groups but it took hours for a client to authenticate and create the groups. I went to linux on the same hardware and it is so much faster it’'s almost unbelievable. I did use it for my test group of about 50 users with 2003 and it was just fine. But once I hit the 900 user mark, it totally bogged down.
I’'m pretty surprised you were seeing that big of a difference between Windows and Linux. The performance should be fairly similar in general. Perhaps it had something to do with your usage of AD? Any more details you can provide would be appreciated.