II have the pleasure of configuring Exchange 2007 for a company that has approximately 100 users. I would like to know what I need in regards to licensing for Exchange 2007 Enterprise for use on an existing VMWare ESX Server 3.5. Since I can load any operating system would you chose 2003 R2 or 2008? We are currently using 2008 for our Domain Controller and the current domain function level is Windows 2000 native. I would also like to know what the recommended memory allocation would be for this many users and approximate hard disk space. Also what type of anti-virus and spam filtering applications would you recommend. Normally I would use MX Logic for the anti-virus and filtering but the costs would be too much on a monthly basis.