Some rare good news out of General Motors boosted the market on Friday, although only slightly, as the Dow Jones industrial average closed at 10,512.63, up a half point for the week. GM shares were up nearly 9 percent on Friday because of reports that its major union may be willing to negotiate health-care costs that the automaker has blamed for holding it down. The Nasdaq went the other direction, closing down .5 percent for the week at 2063.00. The major advertising agency holding companies experienced little movement through a week in which two of three finished with an increase. IPG closed at $12.63, a rise of 7 cents or .5 percent for the week, and WPP, trading on the Nasdaq as American Depository Receipts closed up 1.5 percent at $53.20. Omnicom was down a little more than a dollar for the week, to close at $81.84, a drop of 1.2 percent.