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.
Bought a 2nd hand Saab from the UK last March, 1.9 TDI Sport & thrilled with the car & saved a fortune vis-a-vis buying it here which is unreal given that I have to pay 5.5k in VRT!!!
They are a good purchase 2nd hand imho though I believe the same policy applies to all cars.