Block remote root login via ssh on Ubuntu/etc to keep your server safe

A moment ago I was checking the system logs on my Ubuntu server and found that in auth.log reports that someone was repeatedly trying to SSH login as root. The "root" entry in /etc/passwd is setup so that no password will ever be matched, so perhaps this potential cracker would never get into my server anyway. But the requests are using bandwidth - and what if they were able to figure out a password that would work? Why not just block remote SSH login access to logging in as root in the first place?

VirtualBox running Ubuntu accessing host file system on Mac OS X

I have a few Mac OS X systems, in particular a MacBookPro that my job gave me. 2.33 GHZ w/ 2GB of memory Core2Duo. It's a fine and dandy machine and I'm real happy with the performance of VirtualBox on this system. Since my job is really about facilitating running Java on open source OS's like Ubuntu what I need is for a virtualized OS to feel very responsive. But I also need to compile OpenJDK source on that OS.