How to know the version of the SharePoint you are using

Go to Control Panel -> Add and Remove Programs.
OR, Go to (Windows) Start>Run>
Type appwiz.cpl

Select the product (sharepoint server) and then click: Click here for support.

Or: Under Tasks, Click "View Installed Updates"
Doesn't it answer your querry? :) Window must have popped up and said about your current SharePoint version.