If it's necessary indeed (and you don't give enough information to be sure about that). Be sure you copy exactly the right things. That's only data, no programs (you have to reinstall them). A few important points:
- Be sure you've got all drivers (including those for your motherboard). - With a little bit of luck, the activation goes automatically.
- Remember to install the old disk as a slave, if necessary, but only after everything on the new disk is running as it should.

Afterwards, use disk management to delete the partition on the old disk, make a new one and format it. You can use this 120 Gb as you like.

Hope this helps.


Kees