Sorry I don't have an answer for you, but I do have a related question that would address both our problems (if solved).
I have four Macs and a Linux box. Linux is the router/NAT, and serves addresses in the 10.10.10.x range. One iMac has an Airport card running as a Software Base Station serving a connection to a PB. This loop is in the 10.0.2.x range.
The problem: the PB isn't able to see the shared resources available elsewhere on the network (iTunes music, iChat, printer sharing, etc). These resources are shared via Rendezvous, which can't extend beyond its subnet - in this case, it's limited to 10.10.10.x.
I see two possible solutions: a) reconfigure the iMac to serve 10.10.10.x addresses via Airport, perhaps in the 10.10.10.150+ range, or b) install software that will allow Rendezvous to bridge the networks.
If at all possible, I'd prefer the first option - it seems inherently cleaner, and since it's so simple to reassign the NAT ranges within Linux, it stands to reason that a straightforward solution exists for OS X as well. Unfortunately, I haven't had much luck figuring out where this is defined. I've learned that this can be easily done with either a hardware base station or (likely) OS X Server, but neither one is available to me.
Any clever ideas out there?