Time Capsule Password Problem

I have a 2 year old Time Capsule, which has worked fine and serves as the WiFi source for a 3 year old Intel IMac, MacBook Pro, iPhone and IPod touch.
This past weekend I upgraded the IMac from Leopard to Snow Leopard. While that went smoothly, about 24 hr later the IMac got completely locked up and upon trying to restart it I repeatedly got the universal no entry sign (circle with a diagonal line through it). Of course we needed a file from it and it was late and without thinking I figured I'd just start up the IMac from my Leopard Install DVD. I'd never done this before and didn't realize I had the option just to access Disk Utilities and so I think I essentially did a retro install of 10.5, with the result that the IMac now thinks it's a brand new computer running 10.5. Anyway, I want to access the (hopefully) back up files on the Time Capsule, but it now won't accept the password I have. This password still works for the other hardware, but not now for the IMac. I have tried varying the encryption settings (WEP, WEP2 etc) but with no success. Anybody out there have any ideas? Thanks much in advance.

 

Thanks, that makes sense. I'll read up and try this when I get home tonight.
Does the Time Capsule configuration password have the same range of encryption options as the network password ? And I'm not clear when the TC is requesting its config password and when the network requests its password. The inquiry window (something like "This Network requires a WEP password") seems the same whether it is the TC asking or the Network is asking. Sorry if I am missing the point.

 

Well I tried it and no luck. When I click on the name of our network in the drop down under the Airport logo in the menu bar of the iMac I get a window that says:
"The Network XXXXX requires a WPA password"

It doesn't take the password that I have on file (format is 10 alphanumeric characters) and when I access the keychain on the macbook pro from which I am typing this, the only password for the "Airport Network" is a 5 letter password that was a legacy from the original Airport Base Station that I had that preceded the Time Capsule. This doesn't work. Does this make any sense?
Thanks for any thoughts JediMeister or anyone else has.