I have a WRT54G set up as a Mesh Gateway.  I follow the instructions below link to "Linking HSMM-Mesh into your Home Network" and can access OK the Mesh from my Local Lan:

http://ohiopacket.org/index.php/Integrating_HSMM-MESH_into_an_existing_network

LAN
LAN MODE: NAT
IP Address: 192.168.1.240
Netmask: 255.255.255.0
Gateway: 192.168.1.1
DHCP Server: uncheck

WAN
Protocol: disabled
DNS 1: 8.8.8.8
DNS 2: 8.8.4.4
Mesh Gateway: Checked

An ethernet cable is connected from the Home Lan to one of the the 4 Lan port of the WRT54G Mesh Gateway have internet access on the 3 Lan port free.  Also, ssh to port 2222 and ping 8.8.8.8 and reply OK, ping with domain name is OK, and ping to 2nd WRTG54 mesh by name is OK.

Second WRT54G (HP2AT-LSK2) sees OK the First WRT54G Mesh Gateway and can access OK the Mesh Status and services.  But does not have internet.  The Mesh gateway is advertised OK because on the 2nd WRT54G OSLR Routes shows:

Destination                            Gateway                              Metric    ETX       Interface
0.0.0.0/0                              10.37.118.27 (HP2AT-LSK1)    1          1.000    wl0
10.37.118.27 (HP2AT-LKS1)    10.37.118.27 (HP2AT-LSK1)    1          1.000    Wl0

Is the Mesh firmware programmed to route internet access only through the WAN port or with the Mesh Gateway box checked can detect and route internet through the Lan port.