Ahem... have a good firewall and password there spanky...
Script kiddies are just dying to find a port 21 open.
Okey... here's some hints. First thing if you go to dyndns.com you can get a free dns name for your PC. This means you can enter a name into your FTP program at school and not an IP...
If you are using a router Fantmx is excatlly correct. You have to forward port 21 traffic to your xbox IP... do port 20 as well..
So here's the skinny
You're at school and you type in... hackmeplease.homeip.net
dyndns redirects you to your home ip address
Your router sends that data to the old xbox...
you enter in your default passwords (should have changed those by now!

) and your off to the races!!
YAY!
