I apologize for all the lame answers on this thread
You have ide, you simply take out the old one and reconnect the cables to the new one. I usually mount it first then connect the cables.
From there have to do a fresh installation of I assuming windows xp if you don't have the install disk for your os then you have to buy a copy from some place like newegg.com
Once you install the new os re-install your software and set up your emails and browser links from scratch. all your information will be lost so make sure you write down any passwords or stuff you really need. You may want to burn your emails, favorites, and text docs to a cd so you put them back on the system.
Good luck, you can do it.
Your computer run faster then ever since it's fresh and you will have a better hard drive.