Wow, your computer is dusty.
You can't format the C: drive if you want to keep the XP installation on it. You will have to do it manually.
If you installed XP on D: while your C: drive/partition was visible to XP setup, it may contain the boot files for XP. If you remove that disk, or format it, Windows may stop booting.
TheMajorMMX - Intel P200 MMX @ 225Mhz - V-Tech (PcPartner) Baby-AT mb w/ Intel Triton TX chipset - Nvidia Riva TNT2 M64 w/ 16MB - 256MB M-Tec SDRAM - Still running.....