Other people have to be having this problem, but I'm not finding anything out there on the web on how to fix it. I've found some general info, but nothing terribly specific.
Here's basically what my setup looks like:
Cable Modem -> Linksys WRT54G -> Computer 1
-> Computer 2
-> Computer 3
-> Computer 4 (wireless)
-> Linksys RT31P2 Router with 2 Phone Ports
Connected to the RT31P2 -> Computer 5
-> Print Server (Lexmark MarkNet Pro)
==========================================
You probable found a solution by now, but FYI.
To insure QOS for the phone the RT31P2 is the first router in the chain.
My hardware is similar. Here is my configuration and settings and it is working fine.
Cable Modem -> RT31P2 192.168.15.1, DHCP server for the network
RT31P2 -> computer 1
RT31P2 -> computer 2
RT31P2 -> WRT54G port 1, NOT the internet port
------------------192.168.15.200, DHCP is turned OFF
-------------------DHCP server is set to 192.168.15.1
WRT54G -> computer 3
WRT54G -> HUB
WRT54G -> wireless laptop
WRT54G -> wireless client WRT54G -> eMAC
HUB -> computer 4
HUB -> computer 5
HUB -> computer 6
Note that the internet port on the WRT54G is not used. This box acts as a switch and a wireless access point.