A DVD writer will write to and play back CDs as well as DVDs. You may need to use a different software burning package though. I don't think the Win XP burning software will burn to DVD.
You can get Nero Version 6 for £3.49 plus postage from: click here
Scroll down the page to near the bottom.
Once it is installed you can update it for free to the latest version 126.96.36.199 from click here