I just installed Ubuntu 11.04 (in a VM). How do I set it up to allow me to ssh into it?
(Right now I get "ssh: connect to host x.x.x.x port 22: Operation timed out".)
Installing the openssh-server package which is available from the Software Center will provide the server element to allow a client such as another ubuntu desktop to achieve a secure connection to a 'server' such as your VM.
That's the very minimum. It allows unlimited failed password attempts on a known port. Direct root-login is disabled (you can still su and sudo once logged in). If your username and password are guessable and the Internet can see the server, somebody will eventually break in.
You want to harden it from the standard setup. There are several suggestions here but at the least, I suggest:
They take about 10 minutes in total and you go from a 1/10000 chance of being broken in to a probability so small, there isn't enough paper in the world to write its fraction... Assuming you're careful with your key, it has a password of its own and you don't trumpet your credentials all over the net.
If the computer is behind a router, you'll also want to do some port forwarding. This is router-specific so I'll just direct you to http://portforward.com