Does MOSS 2007 keep a cash of Active Directory as names get added to sites in a
site collection?

Reason for asking is; the "book" icon gets used to find someone when you are
addding a person to a site, or list, or group. When I look at the people I see
in the "book" it shows me people that are no longer in our company and have been
removed from active directory, yet Sharepoint still shows them when you use that
book icon.

Any ideas?