Most people use DD-WRT
to change the code in the router to support bridging. I did this with an old Linksys router and it worked well for several years until the router died. I'm looking at doing the same to a Cisco/Linksys E2300 Wireless b/g/n router as there is now a DD-WRT load for it available.
Also, my previous post was wrong. The bridge is setup on the 2nd router, not the primary modem/router.