Internet redundancy for 1 windows 2003 server using two network cards

I want to have internet redundancy for my windows 2003 web server. I use this server for email and web hosting. Currently this server has two network cards.

I have two different ISP’s. And I want to assign one IP or ISP to one network card and the second IP or ISP to the second network card.

I get the following error, “Multiple default gateways are intended to provide redundancy to a single network (such as intranet or internet) they will not function properly when the gateways are on two separate, disjoint networks…”

Any suggestions what I can do have internet redundancy?

Thank you in advance…