Don't know if you ever got an answer to this question, but LEAP is basically a modified version of MS-CHAPv1
From the "Cisco Wireless LAN Security" book:
LEAP uses 802.1x EAPOL messages, performs server authentication, achieves username/password (over MS-CHAP) as the user authentication mechanism, uses a RADIUS server as the authentication server, and provides mechanisms for deriving and distributing encryption keys.
For more on LEAP, PEAp and the other flavors of EAP:
https://en.wikipedia.org/wiki/Extensible_Authentication_Protocol