How can I share data between vb.net application

My system need user to update resource ,  when one user hold the resource(Sometime they do nothing ) , another user can t get

this resource.

For example Purchase Order System if someone try to close the PO (Whether they do or not ) . Another one can t see this PO

until this resource is free .  --> User A is typing PO data , User B can not see this PO

How can i perform this without created a row in database ?

What should be the best way to do this ?

I use VB.net 2008 + Sql server 2005

Thx