The story goes that, in 10.4, you could set up a LEAP-authenticated wireless network as a preferred network in the Network preferences pane. Some time later (and I'm not sure when, maybe 10.4.1) when you tried to do this, the network would not remember that it was LEAP, and then failed to authenticate.
I recently had the pleasure of finding out about this problem. Fortunately, Apple published a workaround. The short version is to choose "WEP Password" as the security type for the network, then specify your LEAP login in the password field. OS X will interpret this as a LEAP login and use it. Hopefully the behavior is fixed in future releases.

