Linksys → WRT54G+BEFSR41 - connecting different subnets

My current home network has this configuration:

At the moment though, the WRT54G is set at Gateway mode (so I assume it means it's using NAT), hence the computers in subnet 192.168.1.0 cannot access anything in subnet 192.168.2.0 (but the reverse can happen, but only by IP address since I don't have a WINS server ; at least all computers in the entire network can surf the internet).

Once I tried this: I set the WRT54G to Router mode, then defined a route in the BEFSR41 on the LAN side so that computers in the 192.168.1.0 subnet can access those in the 192.168.2.0 subnet (again only by IP address). The problem is, in that configuration, the PPPoE connection (which is managed by the BEFSR41) seems to become unstable and frequently disconnects. Hence I had to go back to the old config.

Is that normal? Has anyone else tried that?

Update: My ISP changed the modem they supplied (used to be a SMC modem; replaced with a much cooler looking one, and they did it free of charge too) after I complained about frequent disconnections (not related to the problem above; the tech guy explained that the old modem wasn't designed for the bandwidth of my DSL subscription plan and the new one was needed). On a whim I tried the experiment again. Now it works better. I guess the DSL modem was the problem.