Caching Active Directory

Question

I want to cache the active directory data i.e Email,firstname and last name two times a day. This should happen behind the scenes maybe in global.aspx application.start(). And now whenevr I want to fetch 1700 (my application allows a functionlaity of browse users) users I would do that from cached data. My code is in Asp.net C#.

Can someone let me know the way to do it.