system partition

Hi i recently reinstalled my windows xp sp3 and i have a problem with how my partitions are used by xp.
I have 3 partitions on my drive. Partition C whichh is used mostly for programs and windows related stuff, Partition D which i use for movies,music etc...
and F is where i put my back-ups(its a new partition i made on this install of xp).
Now on the previous installation of xp the C: drive was boot and system partition and i was happy with that. But now somehow C: is my boot partition and D: is system partition and i don't want that because if i catch a virus or something my D partition is vulnerable too( i had very much trouble collecting my music and movies). Is there a way without reinstalling windows to move the system files that are on D: back on C: and make D: just a normal partition?

 

Changing the drive letter of the system drive could render some of your software unusable due to references in the registry. The easiest solution would be to merge the D and C drive together but maintain the drive letter as D. Using third party software such as GParted, which is free, will make this operation easier to do.

http://gparted.sourceforge.net/livecd.php

I am a bit baffled as to how you got the MBR and the OS on seperate partitions after a re-install, are you sure you have not now got two installations of windows XP. When you boot the PC does it go straight into windows or are you asked which OS you want to boot from?