How to change Booting drive from D drive to C

Hello,
I have got a hp presario dv6000 laptop comes with windows vista installation. It had three partiotion C, and D.
C drive has got windows vista installed. what i did is i splitted D drive in two partition D and E. so now i have 3 partition C, D and E. I disabled sata native support from Bios and installed Windows Xp on D drive. Now the problem is windows xp working well. But i cant get the windows vista. I want windows vista back. And one more problem is i cant see the E drive in my computer. Its not visible.
Can someone plz help in this problem. I will be very greatful to you for any help.
Plz reply as soon as possible.
Thanking you,