Check http://www.craigberntson.com/Articles/kb003.htm

>I got an application in the server, client's PC map 'S' as network drive
>link to the server,
>my system will place in "S:\AcctSystem\"
>
>If that company got 10 PC, they can map the S drive and run the exe easily.
>Now, we need to control the license with 5 users which can login the system
>I got a little idea
>(1) when 1 user login ( increment a field nooflogin in a LoginTable )
>(2) everytime user login (I will check the nooflogin , if the number over 5)
>, reject user login
>(3) everytime user logout the user(nooflogin will be decreased )
>
>Problem : If the user didn't logout very well, ( task manager kill the task
>or PC hangs) that will make the no of login incorrect,
>
>Can anyone give me some idea to do ??
>Thanks a lot