1) Version 3042 is a BAD version of SQL Server 2005 to be on. You are missing some very important updates related to the SP2 debacle(s). See here: http://blogs.msdn.com/psssql/archive/2007/04/06/post-sql-server-2005-service-pack-2-sp2-fixes-explained.aspx. Get patched up.

2) Whenever dealing with MemToLeave issues you probably should be on the phone to Microsoft's Product Support team.

3) 30 databases is nothing. I am supporting 6500+ databases on one server at one of my clients! 🙂 Your 'advisor' doesn't know what he is talking about.

4) Make sure your 32 bit extended memory stuff is set up correctly. Search for PAE and AWE on the web and in BOL.

5) I agree about disabling hyperthreading. Almost always results in better performance.

6) Are you having overlapping backups at all? This is a often a bad thing.

7) Consider getting a pro in to help you through this mess.