Two internet connections one LAN

Hello!!

I have two internet connections and i’de like to know the best way to have both working on the same LAN: (for example)

-> I’de like to have mail server and tecnical department to get out through line1, and the web server and all other departement’s on line2.

what would be the best way to do this:

-> i have the foling material to do it:
– ISA 2004 (1 or 2 servers)
– windows 2003 servers
– two routers
– 24 ports switch with vlan suport.
– it’s important to have only one Domain.

Thanks For Helping !!!!

inneed 4 help