|If the mboard's bios Setup is NOT detecting the hard drive.....|
Some hard drives in older laptops have a gender adapter that's plugged into the pins on the original drive that must be removed and installed on the replacement drive. That's obvious because on the new drive you can see the pins, on the old drive it doesn't look the same because of the gender adapter.
If the mboard's bios Setup IS detecting the hard drive, but your problem is the computer is not detecting a bootable hard drive, new hard drives (or used hard drives that have had their data deleted) have no data on them and cannot be seen by the bios as bootable (having had an operating system installed on them). That problem will go away after you have installed Windows on the drive from the Vista DVD, or after you have installed the contents of the Recovery disks for the specific model.
If the bios Setup IS detecting the hard drive but the initial files loaded from the Windows DVD, or from the Recovery disk set for your specific model, are NOT detecting it...
If the drive is SATA......
This is about XP - it has no SATA drive controller drivers built into it.
Similar applies to Vista - it has some SATA drive controller drivers built into it, but not all possible SATA drive controller drivers.
You can provide the SATA drive controller drivers to Vista on other media other than a floppy disk, such as a flash drive, or you can set the SATA drive controller mode to an IDE compatible mode in the bios.
Installing XP and SATA drive controllers, SATA drives; the SATA drive controller bios settings.
See response 2: