If you want to complete the range of ports you can open basically for a windows 2003 SBS.
Batch Smtp ( For mail ) ( TCP )
25 – SMTP
Remote Workstation and Outlook Web Access ( TCP )
443 – HTTPS (for RWW and OWA)
Sharepoint (TCP )
444 – SharePoint
Microsoft VPN (TCP )
1723 – PPTP VPN
Remote Desktop Connection ( TCP )_
3389 – RDP for remote administration
Remote Web Workspace ( TCP / UDP )
4125 – Remote Web Workplace
All ports are TCand must be enabled in the Access-list and port forwarding some examples for a Cisco Router below:
Static ip forwarding
ip nat inside source static tcp < internal Lan address > 3389 interface Dialer10 3389
ip nat inside source static tcp < internal Lan address > 443 interface Dialer10 443
ip nat inside source static tcp < internal Lan address > 4125 interface Dialer10 4125
ip nat inside source static tcp < internal Lan address > 25 interface Dialer10 25
Access-list
permit tcp any any eq 1723
permit tcp any any eq 443
permit tcp any any eq 3389
permit tcp any any eq 4125
permit udp any any eq 4125