The DHCP section is normally in a section called something like "LAN IP Settings", and in there you could assign a reservation that gives PC1 .X and PC2 .Y addresses.
I've had a similar issue whereby my (USB dongle) wireless wouldn't connect to my WAP1 in the same manner as you mentioned above, although it would connect to my WAP2 fine. As I've run a CAT5 cable between the two routers/locations it doesn't really matter to me, although I would be interested in finding out the cause/solution.
My only thought - which I haven't tried/tested - would be to go into the advanced settings for the wireless connector and manually enter the SSID and key (the hex one, not the passphrase) and see if that works. Having said that I'm not sure whether that's something you've had a go at.
The one other Q I have, is to double-check that when you stated that you have disabled the filter you mean that you have disabled the lock-down setting for the wireless - not that you've blocked that MAC addy from connecting.........?