OK, i will give you a breif explanation. If you need more help, just let me know and i will get into more detail. Restart yuor computer, put the cd in. Then go into your bios and make your cd rom drive the fist boot priority. Then exit and save changes. Then your computer should boot off the cd. Follow the step by step instructions. Install a fresh copy of windows. Then you will see a table with partitions in it. Find the partition then press enter. Formating should only take about 20 seconds. If you just let your computer run off the cd it will install windows xp for you.
Again, i was breif, but if you need more specific diretions, just let me know.