The comprehensive and most convenient method is the Jet User Roster.
Example use of such is in this FMS article and example. http://www.fmsinc.com/free/newtips/access/accesstip2.asp
(Just Googled for a convenient example but Luke Chung does great work ;-)
Bear in mind that it won't give you actual locking detail.
In general that's too brief and intermittant to be of value and depends largely on the host OS too!