Here's a PTM file with county lines. The county line boundaries were imported from a free government source using a modified version of the Spatial Data Importer developer sample originally released by Microsoft in 2001 or 2002.
This PTM file was prepared for a user who noticed that county lines don't show up at the same zoom levels as they had in a previous version of MapPoint. The county lines did not show up when you were zoomed out.
See attached screenshots.
Let me know if you have any questions or special requests! I have a small utility in Excel VBA that can change the line width and color. It could also be used to set the fill (background) color of the county polygons as well as the "ZOrder" (in front or behind the roads). If there is a need for this I can clean it up and post it as a companion to this download.