Sorry about the confusion asyed, I believe I've found a solution for you.
What you'll want to do is (from within the screen designer for your custom screen), click "Edit" on the grid, then click Next to go to Step 2 of 9. You're going to want to Insert a new Column so pick the SalesRep field from the dropdown and click Insert Column.
Next, click on Actions to the right of the top field (it should have Caption "Go To..."). From here, add a "Start Conditional Statement" Action by picking it from the dropdown (it's under ".: ADVANCED :.") and clicking the Add Action button. You're going to want to have "Value From Screen | Contacts:SalesRep" = "Value From Session | User- Sales Rep Initial" in the action properties. Click Save & Close and move this new action to the top of the Action List, then add an "End Conditional Statement" action at the end of the list.
This will allow users to edit customers that are their own, however it will not provide any feedback to the user if they click "Go To..." for someone else's customer. You could add another conditional statement at the end of the action list that says if it's not the user's customer then pop up a message with appropriate feedback.
If you're looking to do a fair bit of customization, you might want to consider a dedicated consultant. They're experts on the subject and can take a lot of the headache out of getting Method to function just the way you want it to.
Hope this helps.
- Justin