These are the specs on my PC stated on the HP/Compaq website:
http://h10025.www1.hp.com/ewfrf/wc/document?dlc=en&lc=en&product=432786〈=en&cc=us&doc name=c00239777

Notice it shows:

"one, 3.5" internal (occupied)"

"one, 3.5" external (available)"

I checked out NewEgg and an external HDD sounds like ****.

If you check the mobo link within the link above, it states it has:

"Two SATA connectors, each supporting two ports"

(what does "supporting two ports" mean?)

I NEVER use the CD-ROM drive, so would it be possible to place an internal HDD where the CD-ROM drive is?

When it says you have 2 sata ports this means you can have 2 serail ata hard drives. this way you dont have to connect it to the IDE cable.

SATA Hard drives

And yes you can put a hard drive where the cd/rom is.. But there should be enough room under the hard drive you have now to put another in.

Waters is correct, you basically have 2 choices.

You can either purchase a normal IDE hard drive and connect it to the same cable that your CD-ROM is running on (yes your cd-rom will still work) or you can buy another SATA hard drive and connect it to the spare SATA connector on the motherboard.

SATA would probably be the better choice as they are the "new technology" so will be faster and are simpler to connect.