For TightVNC (or indeed VNC in general) you need only 5900/TCP. If you want to use the Java/HTTP viewer you also need 5800/TCP but this is not necessary; only 5900 is necessary.
Are you running firewalling software such as the XP firewall on your laptop? If so, have you opened port 5900 on the laptop?
One final note: it'd enhance your security if you abandoned the portforwarding for VNC and instead established VPN access to your SME server, then used TightVNC to access your laptop via the *internal* LAN IP. This also works beautifully with Remote Desktop or PCAnywhere.