Don't mean to be rude but are you certain the jumper settings are right - Master for your original and slave for the second? Have you checked the HD manufacturer's site for the jumper settings, esp the second drive? You could also try setting both to cable select under XP.
Have you interruped the boot up and checked the second drive is enabled in the bios. Usually press del at the beginning of the oot process - you will get a message.
Another thing to check is that the cable is the right way round - red stripe to pin 1 (some old drives (and cables) did not have the lug and cut out)