This is very simple, find store.exe file.
Click right mouse button on file store.exe and choose ??oPropertise???
Click ??oVersion??? and for ??oOther version information??? choose ??oComments???

For Exchange Server 2003 default installation is in folder C:\Program Files\Exchsrvr\bin

For Exchange Server 2007 default installation is in folder C:\Program Files\Microsoft\Exchange Server\bin