OK, fair enough, felicia is a bit more stable in the same way intrepid is, ubuntu seem to be concentrating too hard on the timings. Anyway, the keyring is a secure location for storing various passwords that your apps may need, in this case the wireless password. You can access it directly from Menu --> Preferences --> Encryption and Keyrings. Anyway, I think if you use your user password, it'll be able to open automatically on login (I certainly don't get any popups every time I try to connect).
As for the string: that's a sequence of hexadecimal characters required as a "passphrase" by WPA. If you're having issues with WPA, there's a wiki entry somewhere on it. I think by using a custom, you're using WEP security, so you should change from the WPA in the drop-down box.
As you say though, LM6 doesn't seem to have these problems, so just for future use.
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