First, make absolutely sure that you accidentally overwrote OS X before proceeding. If you did overwrite OS X, you will have to reinstall from your original install DVD set.
Follow along: Step one: Reset the PRAM|NVRAM. See this
LINK.
Step two: Boot the machine with your original install DVD. Remove the Boot Camp partition and then drag the partition line until it fills the entire hard drive and you have one partition.
Step Three: Erase the hard drive and format it as HFS Extended Journaled using the GUID scheme. Name the hard drive "MacIntosh HD". (no quotes)
Step Four: Reinstall OS X and all your applications.
If you have a Time Machine backup you can use it to restore everything during the reinstall process.
As I said above and reiterate: Make sure that you overwrote your OS X installation before proceeding.