Network Airport - no router DNS server IP

Hi,

I'm having a heck of a time with 2 iMacs both running OSX 10.6.8, trying to setup an airport connection to a DSL-604G router.

I think I've pinpointed an issue which is common on both iMacs, and that is in:

System preferences/Network/Airport/Advanced/DNS

On my main i7 Quad machine (a 3rd machine) which works fine, I can see a DNS entry which is greyed out - showing the address of my router (10.1.1.1), but on the other 2 machines this entry is not there. Could this be why I'm not able to "see" my local network and setup my airport connection.

I have tried :-

(auto) DHCP setting

manual DHCP setting

DHCP with manual address

Renew lease

Several new "Locations"

Manual antry of Router IP in the "DNS servers" window

Re entering the wireless network details under the "Preferred Networks" (Airport tab)

Removing the keychain password

Rebooting

. . . and quite a few other things. But still I'm not able to connect to the wireless network via the Airport on my iMac's.

I did see the network appear during one test, but despite me checking this by removing and re-entering it on the "working" i7 machine (which worked fine), the problematic iMac(s) woul not accept the password, or timed out - or both!

Any idea's or help would be much appreciated as I've has this problem previously.

Thanks