Getting past *two* NAT routers

[PicaRules]

Hello,

My DSL is served by PPPoE; the DSL modem is a mini-router allowing only one (192.168.1.2) address. I think I understand the port assignments when a single router serves multiple boxes. But I serve my LAN via a second DHCP server, the Mac OS X box itself (Internet Sharing). So not only the modem but also the main box is both a LAN client and a DHCP server; it doesn't have a "real" IP address to begin with, and in fact is known by two (the PPPoE modem is given the real one). What will get me to the other machines on the LAN? Manual port setting?