How do I add a hard drive?

I am trining to add a HD to my computer SATA how do I do this. The HD that I am adding has OS I should not have to take it off right?

The drive has an OS on it? From the same computer? Is it a desktop? How many drive bays?

Physically, it is a simple task. If the hard drive has a OS installed from a different computer it is unlikely to work. A bit more information would be good to give you more exact help

Monton

The HD im adding is from another computer and it has XP home. The HD that came with the computer has XP pro. It is a desktop, and it has 3 bay drives. if there is anything else you need to know let me know.

Is there a way I can wipe clean the Drive with XP home. would that slove me problem?

that's correct. the bootmgr knows nothing of it and it will be just allocated space (but ALL programs will not be usable)

You don't need to, but can it you so choose. With the drive connected to the new system, you can drag-n-drop files or folders to the system HD, or just access them where they are.