configure two static ip’s in a machine

hi,
I have mail server running in win 2k.I have 2 static IP’s provedide by the same ISP such that one Ip is given from one place having the same default gateway and the other IP from another place haing the same gateway as the previous one using DSL technology .My question is that i have to configure the mail server using the two differnt static IP such that even there is any failure in one of the lines , my mail server still runs with the other static IP running in the machine so that mail server is accesbile to the outside world always.
How to design this setup.if not what is the other possible way.