LEAP is a Cisco product and is not supported on Microsoft IAS servers. See other posts about that. There are only a few RADIUS implementations from other vendors that support LEAP. Cisco ACS of course would work fine.
You can make your 1200 the RADIUS server but it might not be as scalable as you want. If your network is a small one and you don't mind managing the user accounts locally on the AP, I think it would be the easiest.
Otherwise, use some other authentication method that would work with IAS.