Airport keeps dropping IP address/connection

Okay so I've been able to connect to my network with my Macbook Pro (10.6.3) for about a year now with no major problems, heavy activity going through the wireless printer flawlessly - but lately I keep getting, for no apparent reason, the incredibly vexing "airport does not have an IP address and cannot connect to the internet" keeps showing up in the Airport pane, and Network Diagnostics does lip service and not much else ('contact your network administrator').

I've found that after turning the airport off and back on it'll reassign an address on the network, but after a few seconds enragingly drops it again, again for no apparent reason. It's gotten to the point now where I can't even connect to the internet unless I'm hardwired to the modem, such as I am now. Sometimes after being plugged in for a few minutes airport will seem to reinitialize another address and connect, but this doesn't work for another few more minutes before shoved back to the ethernet crutch.

All the standard rote solutions prove useless, I've tried resetting the router, modem, computer, etc all in various lengths and sequences to absolutely no avail. Any help would be appreciated, absolutely at wit's end....