No operating system----- No internal optical drive

I have a dell latitude 2100 laptop I bought that had the operating system wiped. This computer also had no optical drive. I bought an external optical disc drive and hooked it up and tried to install windows. Windows could not start because of a computer disc hardware configuration problem. Simply, windows wasn't installed to read the optical drive's installation disc and the optical drive could not read the windows installation disc because it could not be configured by windows! WOW!!!!! My question is how do I go about getting my vista business reinstalled? I also have my dell reinstallation disc for windows vista business. HELP