Is it the gearbox?

Can you help? Our car started making a whistleing noise last week and we were informed it could be the gearbox or as we weren't having problems putting it in gear it could be the clutch.
Today I have driven the car and it sounded as though something had fell off underneath and was being dragged along the floor as well as the whistleing noise. I got out and had a look underneath but couldn't see anything - the car now struggles to pull away at junctions and is also struggling at gaining speeds. Very nervous about driving now - any info would be greatly appreciated. It's a V reg Zafira 1.6

Nic
August 2010