Upgrading cable modem with built in wireless router

I had a cable modem with built in wireless router. Unfortunately, it did not support the faster wireless protocols. Since I want to use it to stream video from mythtv I needed to upgrade.
Now the simple (famous last words) thing to do was just to get a new wireless router and then just use the old one for its cable modem.
Of course, it isn't that simple. I had hoped I could just take a lead from one of the modem LAN ports and plug it in to the wireless router's WAN port.
What did work was the following set up:

• Set both routers to use the same private network (192.168.0.*)
• Have the modem serve DHCP, with local IP address 192.168.0.1
• Set the wireless router IP address to 192.168.0.50 (really just anything to avoid the modem IP address)
• Turn off DHCP on the wireless router.
• Cross fingers

This seems to work ok. New machines connecting to the wireless router get their IP addresses served by the modem, which happily sets the default gateway, DNS etc correctly.
The only downer is that I'm forced to use the modem configuration for firewall etc. and its firewall configuration is less powerful. Also, it doesn't seem to support assigning static IP addresses in its DHCP set up.