I'm currently at my friend's house, and quickly wanted to install Apache2 on his Ubuntu machine (he's asleep, and I feel like coding). apt-getting everything really wasn't a problem, in fact everything started and worked fine.

I did get a warning though:

apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName

Fortunately, this can easily be fixed by editing the configuration file, usually stored at /etc/apache2/apache2.conf. The fix is simple, and you'll kick  yourself. Just add the following line to the end:

ServerName "localhost"

If you're still having problems, feel free to drop a comment, and I'll get right back to you.