traffic routing

Hi All,

not sure if this is at all possible.

I have a network comprising of a SBS and a hand full of XP pcs. All are
connected to the Internet via a god quality DSL router and all works fine.

We are now implementing a bit of software that downloads data from a
particular source, and can only be accessed using ISDN. A new ISDN line is
being installed with an ISDN router.

Two of the XP clients will be using this software but will also be using the
dsl service for general access to the Internet.

My question is this......

Can these two PCs somehow route all general internet traffic to the default
gateway and have traffic generated by the new software directed to the ISDN
gateway?

Many thanks in advance

Paul