Yes, you can use 2. I'm going to assume the drives are IDE rather than SATA. You should power down the computer and pull both drives out, remembering which was the one were using. Set the jumper on the back of it to Master (it may already be there). Then take the drive your friend gave you and set its jumper to Slave.
Once you have that done, put the drives back in your machine, and connect the IDE cable to both. Power up and you are probably set.
Complications can arise if the drive you were given wasn't partitioned/formatted. But you can fix that through Disk Management.
If the drives are SATA, there are no jumpers you need to worry about, just connect the drive.
To get any performance benefit you'll want to set your pagefile/swap to the 2nd drive, that keeps Windows and the pagefile from needing to access the same drive at the same time.