Those warnings are for a reason. Once you do that, the system is gone.
The proper way is to set you PC to boot from the CD. When it does you get some kind of message, depending on what kind of install CD you have.
Have you already made a backup of any data you want?
In the case of the standard version of the XP install CD, there is the option of instantiation without destroying your documents. Otherwise, doing a format and install destroys all data on the selected partition.
What some do is to use a partition manager to create another partition, format it. Then copy documents to the new partition. Then formatg only the system partition and install.
