The Manufacturer support and warranty periods are typically different between OEM and retail drives. If either the original or new drive (or both) are Seagate or Maxtor, you would be entitled to download and use Seagate DiskWizard software, which provides you with Acronis drive migration and imaging software, at no charge.
You can duplicate the exisiting drive onto a new drive, either having DiskWizard simply installed onto the original drive, or then from within DiskWizard creating a bootable recovery CD, and using that to transfer an image of the old drive onto the new one.
If you can get away without needing the boot CD, you should be able to temporarily connect the new drive in place of an existing IDE CD/DVD drive, and do the transfer, then reconnect with the new hard drive in place of the original. This will involve changing the jumper settings on the new drive (there will be a diagram either on the drive or on the drive manufacturer's website), but you won't need an extra IDE cable.
If the motherboard does have a second IDE channel (most older ones did) and you have available a second IDE data cable, you could have both drives operating in the system together that way.
Some older motherboards have a BIOS issue where they don't operate correctly with a hard drive over 132GB capacity, and may require a BIOS update to overcome this, or if no update is available, use of a PCI drive controller board is advisable. If the existing hard drive is already larger than 132GB, then this probably is not an issue.
Edited by Platypus, 02 June 2008 - 09:59 PM.