i have had installed 7
fluxbox, gnome, kde4, xfce, lxde, icewm, e17
all will be available in the login menu under the session button, click on one and log in, log out and select another
you can have 2 or 3 loaded simultaneously if enough ram is available
celerons are some of the worst cpus i have use and overclok them makes them more unstable, in linux they perform way better than on windows but still overclock such cpu sounds like a bad idea but that is just my personal opinion