The steps are:

1) Set up a VNC server on your Home PC
2) Allow Access through you Router and possibly your firewalla

3) Make sure you can connect to your router from outside you network. You need a static IP address for this (think of it as your networks postal address), or a free service like dyndns.

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1) http://www.dyndns.com/support/kb/tig...ick_guide.html

2) http://www.tightvnc.com/faq.php#vista

3) The same as 1

See also:
http://www.petri.co.il/remote_window..._using_vnc.htm