DHCP isn't working because there is no communication between the NIC and the AP.
You'll need to get that fixed, first. There could be any number of reasons, but that there is no trained SSID shown when the nwid is set to "" tells me to look for a functioning AP. Does it broadcast its SSID? If so, it should appear in a scan: "#ifconfig urtw0 scan" -- if nothing shows, yet your PCMCIA card works still, then perhaps you might have a bad USB NIC. Might.
Me, I'd set up a broadcasting AP with no security, first, just to test connectivity.