Help! How to get my external disc drive and iMac talking?

My iMac disc drive is broken and I need to upgrade to Snow Leopard OS because Safari is no longer working, it will only load 2 sites before freezing and won't play any streaming videos. The rest of my computer works fine. I bought a Samsung USB 2.0 Ultra Portable External DVD writer model# SE-218CB/RSBS, but the computer is not recognizing the device. The troubleshooting said to re-install the OS, but I can't do this without a disc drive. Is there another way around this to get my computer and device to recognize each other?