well basically theres 2 main types youd be looking at, IDE (or ATA) and SATA
ide is the older sorta type, although i think new motherboards also support this.
sata is newer with faster speeds etc, only newer motherboards support this.
when did you get your pc / what are your specs, this might help to tell which you have.
you can tell through windows, go to run, type "msinfo32" on the left u see components, click the plus, then click the plus on storage, then click disks.
on the right hand side it'l say model. mine says hitachi HTS541612J9SA00. ok now open google, and search exactly the model.
heres mine for a example. see first result it says its serial-ata 150 (SATA).