alias ip and natd with ipfw fwd

[G Bryant]

Not sure if previous posts came through, so please forgive if this is a 
repeat.

Can anybody please help with problem.
Using natd and ipfw and trying to fwd packets to a non-default router 
out the same interface.
Currently using alias for the second ip, but it doesn't seem to be 
working for some some reason I'm missing. Would clone maybe work?
Any advice would be appreciated.
Thanks Graham