Actually, the very first attached image in the thread is of the Airport's security setup. There is only one option, and that's what type of encryption to use.

Mark, I just think that the security in use by the Airport is what is causing the problem. If there is no security on the Airport OR the Linksys, everything works perfectly, just as it should. But the second that I try to set up security, it all fails.

Oh, and I'm using DD-WRT version 23 sp2. That would explain why I'm not seeing "repeater bridge." If that truly is WDS, like Tom is suggesting (although there's a whole separate WDS section), then I hear that this severely cuts down on the wireless transmission speed. By half, right?

Another question: should the Linksys have the same SSID as the Airport. I guess it doesn't really matter, since it's not set up (in my case) to share a wireless connection, but I thought I'd make sure.