Installing Mono on Fedora Core 3
There is a great (and brief) summary of how to install Mono on Fedora Core 2 (but also works on 3) here
on Equivocal Rambling. The only thing you need to do differently is set up the yum channel in yum.conf like this:
[mono]
name=Mono 1.0
baseurl=http://www.go-mono.com/archive/1.0.6/fedora-3-i386/
gpgcheck=0