You need to fit an IDE drive as a 2 year old PC won't have a SATA connector.
7,200 refers the revolutions per minute and is considered fairly fast.
8.4 ms refers to the typical time it takes the heads on the disk to position themselves to start reading the data (access time).
Ultra indicates the connection between your PC and the disk is fast but in practice probably makes little difference.
Any IDE disk you buy should work with your PC.