Updating Databases

i'm very new to asp and databases too.  i was following along with the asp/database tutorial here: http://www.webwiz.net/asp/tutorials/updating_data_from_database.asp

i found myself wondering what would happen if two people were trying to update the same record at the same time.  i know there is some locking going on in the example code, i'm just not sure what it's locking.  can someone identify which parts of the code (if any) would prevent two people from trying to update the same record at the same time?

to be sure i'm making myself clear, here is the scenario i'd like to avoid:
user1 opens record1 for updating and begins editing.  while user1 is editing, user2 opens record1 and begins editing.  while user2 is editing, user1 submits his/her changes.  the database is updated with user1's changes and user1 walks away happy.  then user2 submits his/her changes and the update is successful.  user2 walks away happy.  latter in the day, user1 re-examines record1 and finds that the information he/she submitted is not there.  user1 schedules an appointment with his/her shrink because he/she thinks he/she is losing his/her mind :)

is there some way to prevent user2 from opening record1 when user1 has it opened?
tia

Thank you very much for your explanation and suggestion.  I really do appreciate it.