hard disk help

[Road2Ruin]

I have an old hard disk with lots of data on it. I have now bought a new machine and installed then old hard disk into it. Windows Vista will not recognise the old disk. It is there in device manager and also in disk management but it wants me to format it as though there is nothing on it. How can I access the old data? To help I am not sure the full capacity is being shown on the new machine, I think it might ne asking me to format the unsused part of the disk but I cant take that risk. Could it be that the data on the disk is encrypted by xp as part of the user profiles and so is only accessible by that computer?

any help greatly appreciated.

Peter