I am using Ubuntu 12.04 LTS. I installed the Monaco font from here. The font is visible in Font Manager. I can also set the font in GVim.
However, if I try to set this font in GNOME Terminal, that is not possible. It is not listed in Edit > Profile Preferences > Font.
I was facing the same problem with 12.04. Remove your previously installed Monaco fonts. Install Monaco fonts available here and try again.
It worked for me.