Well for one thing, if you want a total format, use the 98 Boot Disk method. Pop the 98 boot disk in and Start with CD Rom Support.
Then when you see the A drive, if you want to delete partions, type "Fdisk" if you want to format each partion, do this:
1. Type "format c:" , For the Second Drive type "Format d:" Also, the RAM is considered a drive in DOS. Which will probably be e:
But once you have everything strait, goto a computer with internet access, and download the Setup Disk's for what version of XP you have. After the format, pop those inand install XP again.
Links:
98 Boot disk Download Windows XP Setup Disks