Move Exchange database to new hard drive

The hard drive on the our server is full so I would like to add a new hard drive and move the Exchange databases to the new hard drive. We are running Window NT server and Exchange 5.5. We only have about 25mb left on the hard drive and are havingproblems with email. It will lock up or not let us send mail until we reboot and then it will be ok for a day or so. Do you think these problems are due to the low amount of disk space? What steps do I need to take to move the Exchange databases to the new hard drive and about how long it will take. The priv.edb database is about 4GB.