Also, thinking about this, make sure that you don't have two identical IP addresses in your network that could be seen from any point.
ie, your main router is probably
outside IP (assigned from DSL)
inside IP - 192.168.0.1
and then your secondary router should be set to
outside IP - 192.168.0.xxx (assigned from router 1)
inside IP - 192.168.1.1
Then use a subnet mask of 255.255.255.0 on all machines, and for machines on the main router use a default gateway of 192.168.0.1 and for machines on the secondary router, use a default gateway of 192.168.1.1
This SHOULD help clear a lot of things up. SSL and some encryptions may have some problems, though as they may interpret the two 192.168.x.x routers as a "man in the middle" style attack. I'm not sure, though. I've never tried to segment 192.168.x.x network like this. I'm basically giving theory.