Have you tried looking through the settings for the connection manually on the 770 (as if you are going to edit them) just to see if anything looks weird?

Maybe also try deleting the connection and then manually re-entering it on the 770?

Yes, I've done this too. So I'm really stumped. The only way to find out if my router is busted is to try a new one.

Have you tried it without using wep? I also have a wrt54g v2 with dd-wrt firmware, and i have no problem at all, using WPA. You really should not use WEP because it's to easy to crack.

Try doing a factory reset on both devices... then it should work. Then gradually increase the security settings until it stops working or until you are happy with the security level.