Opportunistic File Locking

I am trying to figure out opportunistic file locking. I work for a company that is running an older app in visual basic and the vendor says that each work station must have opportunistic file locking turned off. I think I turned it off on the server but the vendor swears that is not good enough. I’ve read the article here: http://support.microsoft.com/kb/296264 but am still confused. Is there an easy one step answer? I’m running the clients in a mixed environment of 2000/xp and the server is server 2003 r2. Thanks.