If you bought a PATA drive you may have to dive into the machine and learn if you have an PATA IDE connection you can use.
I just got a new Dell that only has a cd-r/dvd combo drive. I had recently purchased a Samsung dvd-r/etc. and put it in my old HP computer. When I took it out of the old one and attempted to install it in the new Dell I ran into a cable problem. The Dell combo drive does not use an IDE connector, it is something much smaller (about the size of a USB but not a USB connection). The IDE cable that is running to the front USB ports in the Dell doesn't have a spot to connect another drive to it. Any ideas on what this other type of connector is and how to solve the problem?