Can't you just assign a second IP to the empeg? Let it get the first one via DHCP and then do something like...

ifconfig eth0 add 192.168.102.3 192.168.102.254 up

from init or another script? I haven't actually tried this on an empeg, but that would give you two IPs on a normal linux box IIRC. That gives you an eth0 and an eth0:1 so you are technically on both networks at the same time.

-Mike
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EmpMenuX - ext3 filesystem - Empeg iTunes integration