I've had similar problems with my brand new AT&T 3800HGV-B uverse setup. 

All of the Apple products in my house stopped working -- the Mac mini running 10.5, the Macbook Pro running 10.5, the iTouch, and the iPhone 3G. 

I ran iStumbler to swtich to the least conjested channel in my neighborhood.  Nothing.  I switched to 802.11b from 802.11b/g.  Nothing.  Neither the Mac mini or the Macbook Pro was able to get a valid IP address from the DHCP server on the router.  I flushed the cache on the Mac (dscacheutil -flushcache).  Nothing.

I ended up rebooting the 3800HGV-B and that fixed the problem.  But I have a nagging suspicion that problem is going to show up again in 5 days.  That's how long it worked after the initial install before everything went bat-crap crazy.  I set the DHCP lease on the router from 24 hours to a larger value in an attempt to stave off the inevitable.