I don't have redhat. Can I use a redhat rpm?
 

I want to install FVWM and I can't figure out how to compile the source (./configure && make && make install?) so I was going to use an rpm but they only have rpms for RedHat on the FVWM site. Will I screw up my system by installing an RPM for RedHat?

"Will I screw up my system by installing an RPM for RedHat?"

No. A Red Hat rpm is less likely to work on Mandrake than a Mandrake rpm, but if it doesn't work, no harm done. Just uninstall it if it doesn't work.

Sometimes RPMs install into different places - for instance, I tried to install an RH rpm file onto my Mandy system and it installed in into /opt instead of /usr. It worked, just, but some functions took some tweaking since it couldn't find the correct elements - they were present, just not where it thought they should be!

from here:
 

http://www.fvwm.org/download/

you can download the source and compile if yourself on your pc. Then is should install correctly.

Medic6666

# Guides to software and installation and uninstallation
LNAG - How do I install a program I downloaded from the Internet?
Rute Guide's software explanation
You might want to check out CheckInstall to manage source code installations/uninstallation