Simply put a hard drive is a hard drive as they store data.
But the connection of the hard drive to your computer is different.
Home PC's will use an IDE connection as its cheap and suits our needs perfectly. These types of hard drives have a speed of 5400rpm and 7200 rpm. The faster the speed generally the better performer.
They also have a cache buffer, 2MB and 8MB. A cache buffer is temproary storage space that holds information whilst the drive is being written to. A 8MB cache buffer is better as it gives a little more performance over a 2MB one.
Now a SCSI drive is meant for servers as the speeds of these drives are 10000rpm+ and the data can be wrriten and read from much quicker. It's a little over kill for the home user. There also more expensice.
Now a 7200, with 8MB cahe is just a little of the performance of a SCSI.
So i would say go for 7200rpm drive with a 8MB cache IDE drive and you can go wrong.
Drives to use? Western Digital, Maxtor... click here click here
There is also another type of hard drive called a Serial ATA (SATA) but if you click here you'll find many reviews and when i last read a review, there's nothing to jump about - no real gain in getting one of these drives. Also you would need a converter as the connector is different.
Any drive your thinking of buying pop the name in here click here and see what they say.