New Internal Hard Drive

Hey,

This is a smiple question, I have a Dell 4600 Desktop PC , and I have had the same Internal Hard drive running in to for at least 7 years. Before it ever dies, I want to replace it with a new internal drive. I was looking at newegg.com , but they wont tell me what will witch ones work for my PC. I like western digital, Anyone have any idea ?

Oya before you ask , Dell was no help. I sent them a email with no responce.