It's always a good idea to check if a package you want to install is available in the distro's repositories before getting from an outside source. Just my opinion of course.
I saw this link on changing the default terminal in fedora 16
How do I change the default terminal in Gnome3 F16?
The terminal in question in the article is aterm, you'll just substitute it with mlterm.
PS: Also, check the README or INSTALL files from the source package of mlterm, it may have that information on making it the default terminal and/or check the manpage of mlterm after the installation as well.