it displays in the title bar of the 6.5 console. Otherwise, if you open up the 6.0 console, it should show up in the right hand corner of the title bar. In addition if you look at the update\install additional solutions field, you should (by selecting one of the fields) be able to tell what KB hotfix number you have installed (and which is the latest update available). It should also show in Add\Remove programs on the server.
If you look at this article -
Altiris KB24469, it lists all versions, with links to the various release notes.