If by any chance you happen to be trying to get a Ubuntu system (or probably any Linux system) to talk to an Apple Airport (in my case the original 802.11b UFO style), don’t try to use the plain ASCII password for the WEP key – Linux and Apple seem to have different algorithms for converting the password to the actual HEX key.

Instead, open the Airport Admin Utility, double click on the base station in the list to open its configuration interface and then choose “Network Equivalent Password…” from the “Base Station” menu. Enter the hex key it gives you into the Ubuntu networking dialog as a Hexadcimal key type.

Alternatively, just enter the HEX password as the value for wireless-key without prefixing “s:” in /etc/networks/interfaces

The same technique will also be very useful for problematic Windows boxes which seem to have a different text to HEX algorithm to Apple as well.