I administrate a Windows Server Update Service server as know as WSUS server and I had to do the usual things with the update packages as approving and declining. Because I allowed to WSUS to downloading updates for MS Office 2010 therefore relative huge ammount of updates I had.
I started to select them but I did not know which version of MS Office 2010 I have.
I have Windows XP. I made a click on Start menu and I chose All Programs and I browsed Microsoft Office shortcut from the others.
I started MS Word 2010 and I pointed to the top-left positioned File menu.
Here I found the Help option and I beheld the release information on the left pane. (Below you can see to enlarge just click on the thumbnail.)

That was all, finally I have known what is the version of my Office.