2001 Volvo XC70 Transmission problem

I went to an auto auction and bought a 2001 volvo xc AWD V70 cross country. After paying for the car, I took it for a test drive around the auction parking lot. I noticed that for the car to move forward, you had to press very hard on the acceleration pedal for it to start driving. I took it to a mechanic to see what the problem was, and he said it was it's trasmission. My question is, for this type of car with AWD trasmission, what parts including the transmission will fix this problem since it has to deal with the rear wheels too, and also the machanic mentioned about a long shaft that goes to the rear. What parts given the entire transmittion is bad, do I need to fix this problem? Do the parts all come together as an assemble or your have to buy seperate ones? Please send some pictures of the parts. Thanks