Unable to download or update software probably due to deleted files

In an effort to free up space on my MacBook I deleted a number of files. Unfortunately, I was over zealous and deleted my startup disk - I think. I have tried to intall my Mac OSx Snow Leopard using the provided disk but I receive a message that the disk is not recognizable. I have also attempted to download updates from the Apple Site only to receive a message that the download is not able to mount. Any suggestions on how to repair this.