Help with my '99 petrol Vectra!?!?

I have recently purchased a 1999 T 1.6 vectra ls with 12 months MOT and am having problems before I have been able to take it home. I feel however that it could be possible that I am getting messed about due to a much better offer being placed. Apparently the vehicle needed a new clutch and was towed to a mechanic to sort the problem. Before any repairs were made the car purred v.smoothely indeed but now this is not the case and now the dealer is blaming the mechanic for doing something to the gearbox. I really like the car and for sheer principle I do not want to back down and take my money back. I bought the car over a week ago should it take this long to sort the problem? Should I have the car towed to another garage? Are there 2 different clutches for the vectra, could they have fitted the wrong one? How complicated is it to change the clutch and going on what I'm hearing, the gearbox as well? Please help?