Hi,
folks
I dont know much about nt server, if your database is in nt server and .
if we know the user is connected to ur system through some dlls u may be able to know whether any user is still connected to user.
I think we have this option in nt server to know whether any one is connected or not.

Second option

Before taking the backup at a particular time just try to open the database in exclusive mode. If any user is connected to that particular database, this will result in error. You can trap by this

********On error statements
Open database sample exclusive