BRL,
I am guessing your friend gave you the hard drive after he wiped the drive. For the drive to be bootable, it needs to be Partitioned (and made active), Formatted, and have the bootable system files on it.
If you have a Win98 computer, you can make a bootable floppy and load fdisk and format on to it. You can use that disk to make your new hard drive bootable.
If you are running WinXP, you need to put the WinXP CD in your drive and boot from the CD and to a fresh install. (The WinXP CD will partition and format the drive for you, so no floppy needed.)
Take Care,
Richard