Won't connect to WEP secure router

On the MPB, enter the password with quotation marks, like this: "pw123" or "password12345" (depending on whether you're using 40-bit or 128-bit encryption).

See this: http://support.apple.com/kb/HT1126

I had the same problem with my MBP

Here's how I fixed it:
- I SKIPPED the network setup assistant.
- Instead, I used native system preferences, then clicked network.
- I clicked the + sign to add a network
- Typed in SSID of my home wireless network
- (IMPORTANT) in the field below, I was able to specify 128 bit WEP hex *** HOW COME I DIDN'T SEE THIS OPTION WHEN I USED THE NETWORK SETUP ASSISTANT? *
- applied the changes, and I'm on.

Sounds like the network setup assistant has some limitations?

Happened to me also changing from WEP to WPA. You just have to go to Keychain Access, find the stored password en delete it, then select the wifi network and enter the password again, or change the wifi network name in the router. It's a Leopard bug, it just doesn't consider the posibility of changing the security system keeping the same name.

Type a $ in front of the password.