Microsoft CRM3

Just set up Microsoft CRM 3 on our SBS2003 server.

I can logon to CRM on the server and out local network ok but when I try and connect to CRM out the office ie at home iam not able to

I have opened port 5555 on my firewall I type in http://xxx.xxx.xxx.xxx:5555 (xxx as being my external ip

OWA works fine using the same ip

internally i type 192.168.16.2:5555

I am sure its a setting in IIS I have missed but IIS is not my strong point

can anybody point me in the right direction