how to lock an ms access table during insert in order to increment a variable and save it in a multi-user environment

Hi,

    I am making a real estate software and i need to find the next property id field value just before inserting the record. To do this i need to lock the table and find out the property id value depending on whether it is a newspaper lead or website lead. for eg. if 2 users press the ADD button at the same time then i display the property id value of 18 to both users. But when they save the  form at the same time then the first user gets the property id of 18 and the next user gets the property id of 19. This is is possible ony if i can lock the table and find the property id value before insert. I am using visual studio 2010 and vb.net with ms access

Please help with Code in vb.net

Regards

Sanjish