Hmmmm... are you using an Apple access point? I found a discussion that stated the bridging functionality only worked when using the Express as an extender to another Apple access point.

http://www.macosxhints.com/article.php?story=20040927125820995

I also found another discussion that said the WiFi extension will work with *some* gear other than Apple's. It's based on some sort of quasi-standard.

Edit: http://www.gizmodo.com/archives/why-appl...orks-015834.php