Here's a small handy (but somehow evil) software tool I found recently:
It allows to tunnel a TCP/IP connection through Skype, making use of Skype's firewall-breaking capabilities. There is a windows and a linux version and sources are available, too.
Have a look here:
http://artax.karlin.mff.cuni.cz/~vernj1am/index.php?action=static&spec=download
