Have 2 Vista installs - How do I delete one?


I am new to this site. Found it with a Google search. I am not sure that Easy BCD can help me, but even if it can't maybe someone here can point me in the right direction.

I have a clean vista install on the C: drive with no programs. I also have a vista install on the D: drive ( a separate disk drive) with all my programs installed. I want to eliminate the C: drive install and just use the one that is now on the D: drive -- it would be find for it go back to being the C: drive.

This is how got to where I am:

I had to change motherboards, cpu, and memory. New motherboard had different chipset so Windows Vista Ultimate would not load. Since I did not have a current backup of the C partition when the old motherboard failed and I did not want to loose data and have to reinstall all of my programs - I did a clean install on a new hard drive. I activated the install and Vista loaded, but of course I did not have any of my programs installed on this new version of Vista. I read that I could use the repair function on my retail version dvd to restore my old version of Vista. I did that and now I have the new install on C partition and my old install on D partition. Both have been activated. When I boot I get a screen that allows me to choose which version of vista I want to boot into. The default is the new one on the C partition. I would like to eliminate this version and just use the one that is now on the D partition since it has all my programs installed. Of course it also has the drivers for my old motherboard as well as the drivers for my new motherboard. I do not know if this will cause any problems. Any suggestions of how I should proceed from here? Can I use Easy BCD to change my now D: drive to C and then take the hard drive that contains the new install out. Will all my partitions go back to the letters they had before all this began? Any help will be very much appreciated.
Partition letters are virtual, not physical. Just entries in the registry of the runnning OS.
Each Vista will see itself as C when booted, and the other HDD as notC if they were independently installed.
If both OSs are independent (with their own boot files), then just change the BIOS to boot from the prefered system and do what you like with the redundant one.