I am wondering how I can setup a SBS2K3 server to use 2 network cards?

I would like this server to have one internal network IP address (192.168.***.***) for local access on the local network with Exchange, Quickbooks, and network access.

On the second network card, I need a ISP assigned IP address (68.227.***.***). This would be for people outside of the office to access the server and connect to their computers remotely.

I've set up the server like this and it will function ok sometimes for a few days and then the ISP assigned IP address will no longer work. I also get an error if I try to assign 2 IP addresses to two network cards.

Warning - multiple default gateways are intended to provide redundancy to a single netowrk (such as an intranet or the internet). They will not function properly when the gateways are on two separate, disjoint networks.

Not sure why SBS2K3 cannot use two network cards, i've done it before on a Linux machine as well as Windows XP without any redundancy issues in the past.

Is there a work around to this?