Whats the best way to determine what patches/hotfixes are installed?Will the version numbers be different between clusered and non-clustered systems?

To the best of my knowledge there are no different version numbers with clustered and non-clustered systems. There are different procedures for upgrading, such as using the Cluster Administrator to upgrade the Exchange virtual servers. I usually look at the build number and the upgrades in Add / Remove Programs with Show Updates selected.In larger installations you would use tools like those from Shavlik to determine patch levels (we do).How to determine the version number, the build number, and the service pack level of Exchange Serverhttp://support.microsoft.com/kb/152439 Build numbers and release dates for Exchange Serverhttp://support.microsoft.com/kb/158530/MCTS: Messaging | MCSE: S+M | Small Business Specialist

Just for supplement, a similar thread:http://social.technet.microsoft.com/Forums/en/exchangesoftwareupdate/thread/1b8428c4-724e-49cd-8536-5fdea9eee4db