If your file system is fat32 and not NTFS then you can use a win98 start up disk. Just pop it in and pick start with cdrom support. At a:\ type a:\ format c: and enter.
If it is NTFS then;
If you go into your bios and then to advanced cmos. You will then have to change your first boot sequence to cdrom. Save the settings and exit.
Now start your machine with the X\P disk in. This will start a new installation but it will also give you the option to format.