A windows XP can concurently update only 10 clients at a time, So do not put more than 50 clients behind a XP GUP or else there will be delay in updattion. Only Server class OS 200 machines are optimum.
Liveupdate Server--If you mean by LUA (liveupdate administrator) it will support any number of updates but it is highly not recommended as it does not use Delta definitions, every time client will download full definition from LUA.