Re: old computer xp new computer windows 7
If the hard drives are both SATA then you should just be able to plug the old drive into the new pc and it should recognise it and show up without an issue. You should then be able to copy whatever you need across.
If it's an IDE drive in the old machine and the new one only supports SATA then you'll have to either purchase an external enclosure, or put the drive in another machine to transfer the data across.
Of course, I'm assuming in the above that the old computer is too messed up to power on and transfer data which may not be the case. If it isn't then you should be able to either transfer files across the network to the new machine, or just transfer whatever you need on an external drive / USB thumb drive. What exactly went wrong with the old PC?