Routing With Two ISPs?

[Drew Tomlinson]

I have a 4.8 box serving as a gateway with two connections to the
Internet.  Is there some way to set the box up so that packets are
routed out through the same interface from which they arrived?  For
example, if a connection is initiated on port 80 from a packet arriving
on one interface, is there a way to make the outgoing packets from my
web server use that same interface as a gateway instead of the default
interface?

Any suggestions appreciated.

Thanks,

Drew