Saab and Vauxhall/Opel are owned by GM (for now, anyway: there are a lot of rumours about what GM will do with its European subsidiaries). The Saab 9-3 and the Vectra share a chassis.
With regard to Punto engines - i'm not so sure about that.
Saabs are great cars to drive, very reliable,, and they look great but the resale value is pretty poor.