I should add that I want them to see all POs ....just not update all POs.
You should be able to accomplish this using document type setup.
When Security Level = Public ( or others such as Purchasing for the Purchasing department, Hierarchy for Approval hierarchy, or Private), and Access level = View Only, only the owner/Buyer of the document is able to modify while others can only view.
This will apply to both the BWC and the core Purchasing forms.
Additional information is available in the Purchasing User's Guide.
Hope this helps.