UAC and LUA are separate things. LUA stands for "Limited User Account" and the term has been around since the 2000 days at least. All it really means is an account without administrator access. 2000 started adding the "Run As" concept to allow for easier LUA usage. (Unix world, su equivalent)

UAC (User Account Control) is new to Vista, and was called UAC before the OS was renamed from the Longhorn codename.