Because of availability and a lack of general consumer knowledge, internal hard drives can be quite a bit cheaper than standalone external hard drives. You can take advantage of this by plugging your new or extra internal drive into a hard drive “enclosure,” and then connecting it to your PC using a standard USB or FireWire (IEEE 1394) connection.
For this demonstration, I’m using a Western Digital 120 GB internal hard drive and a Cosmos Super Link 2.5-inch USB enclosure. You can mix and match just about any hard drive and enclosure, but check their websites to make sure they’re compatible, just in case.