When I opened lyx again, beamer does not appear in the Doc class choices although it does appear in the Tex configuration.
You need to have a LyX .layout file corresponding to the class you're installing.. the .layout file needs to go in your .lyx/layouts/ folder. Luckily enough, the beamer class author does provide the LyX .layout file along with the tarball.. check in the lyx (or maybe LyX, can't remember) folder.. put that in the folder mentioned above and you should see it in the dropdown menu (I don't think you need to run LyX's reconfigure for this but if it doesn't appear, then do try running reconfigure)...
nirmal
