You can try Teamviewer to see if it does what you need - I think it is also available through the Ubuntu Software Center. If not, here is the product website:
http://www.teamviewer.com/index.aspx
It works through firewalls, and is free for non-commercial users. They have clients available to run on Windows, Linux, Mac, and even iPhone.
Client, P2P I'm sorry but what's ssh? I'm not really Linux l33t, I've only just started using Ubuntu.
Okay that's strange, Linux and Ubuntu aren't in my spellchecker's dictionary, but l33t is.
