Missing window managers?

My linux machine (Mandrake 7.2) froze up the other day and when I rebooted
it, X now gives me the choice of KDE or Default window managers -- all the
other ones are missing. Even more strangely, choosing KDE actually gives
me icewm.

How do I put the other windowmanagers back in the list?

Alternately, from a non-X startup, how do I start X and tell it which
window manager to use?

Or... where do I start to look for the answers to these questions?

\\/