1) Acquire Mono 2.6.7.tar.bz2
2) Extract it:
# tar jxvf mono-2.6.7.tar.bz2
3) Change everything to belong to root:root
# chown -R root:root mono-2.6.7/
4) Change into newly created directory:
# cd mono-2.6.7/
5) Configure, build, and install it:
# ./configure -prefix=/opt/mono; make; make install
6) Add the path to ~/.bash_profile or something as effective.
Since I started out working with a CentOS 5.4 VMWare virtual machine, I had to modify the instructions I found here.
I got my source tar.bz2 from Novell here.
Good link for building Mono for ARM here.
