if you are suing continuous forms then you can't achieve what you want. The Access Form designer treats all the records controls as the same. so you can't lock / unlock one record and leave the rest 'free'
You could, say, select a record bring up a popup modal form to allow edits to that specific record, leaving the continuous form locked. Thats about as close I think you can get.
However could I ask why you want to this?
By default Access forms only ever allow you to edit one record at a time. if you click off the edited record it automatically saves the changes. AFAIK it only attemtps to get a record lock when you start to make changes to the next record
What design requirement are you trying to meet with this?
What form of recoird locking model are you deploying with your application?
The user selects some criteria in a couple of drop down boxes and then opens a form that displays all of the stock we are holding based on this criteria. For example, they select motherboards in the drop down menu and then the form displays in datasheet view all of the motherboards we have in stock.
I don't want this data to be accidently edited so have locked the fields in this form. However I would like the user to have the option of selecting one of the records and editing if need be.