SBS 2003 Allow Internet Access Only

We are using SBS 2003 with ISA 2004 and using 2 NICs. The Server runs DHCP. The internal LAN uses 10.10.10.x. The External LAN uses 192.168.16.x with a Linksys E4200 router connected to the cable modem and it has an IP of 192.168.16.254. We have 5 Static IPs available if that helps.

We would like to have Guest Internet access available to laptops and phones where they have no access to the internal network. How should we set this up?

Thank you.