I did a clean install of OpenSuse 11.3 a couple of weekends back. Everything is working great except the SSH server. Once I installed ssh, it appears to accept my connection, allows me to log in, and then freezes Putty, not allowing me to type anything into the terminal. If I wait several minutes, I'll get a message saying that the connection was closed. After that, the server won't accept connections.

Sometimes it'll start accepting connections again, but after a while, the connection will close on its own. Other times, I will be unable to get a connection until I restart the server.

If you guys needs any more information, please let me know. What could be causing this odd behavior?

Have you tried any other protocols like telnet, ftp/sftp, rpc, etc.? Are the issues you described unique to ssh?

Are there any errors or information in /var/log/messages related to ssh?

I have not tried any other protocols. However, looking at /var/log/messages was most interesting.

It seems that there is an ip address that's very adamant on getting into my box, trying all sorts of usernames. I found another ip address that tried a couple of times, but this one has at least 25 attempts. Would it be possible that the ssh server is temporarily closing the connection due to the amount of unsuccessful login attempts?

It is possible. To disable this pseudo-hacker, for every IP address you wish not allow to connect to your ssh, make:
Or better, DROP every INPUT and FORWARD connection except these you needs. For more information read some firewall tutorials.