Removing the boot drive/vista

Hi,
I need some help to remove the boot drive from my pc. I currently have Vista installed on the c: drive and later I added a new hd and installed XP. I didn't do it the correct method where you hide the boot partition. So both OSes boot from c:

So... I want to remove the physical c: drive (old 80gb) along with vista and keep only the d: drive (new 500gb) and xp... btw there is only one partition on each drive.

although everything works fine, having two drives in an XPC shuttle produces too much heat and fan noise...thus wanting just one drive.

thanks in advance
hank