You would have to install it in a subfolder. So http://www.momfever.com/blog/ for example.
Multisite, however, is pretty straightforward once you do it. It's one of those annoying things, where the second time is easier and we wish we could do it first If you already have WP installed (which you do - http://www.momfever.com ) then you can just add this to your wp-config.php
It should be above the "Stop Editing Here" line.
Then just follow the rest of the directions here: http://codex.wordpress.org/Create_A_Network#Step_3:_Installing_a_Network
I will note that it'll tell you that you have to use subdomains, since your initial blog has existed for more than a month. That's okay! You can add a subdomain and point it to your primary site (see http://elftest.net/multisite-subdomains-wildcards/ if you need more directions)