Removing Vista From Dual Boot (Vista on C:\; Win7 on D:\)

Greetings,
I installed Windows7 as a dual boot on a Vista computer. Windows7 is the
default operating system because it is listed first in the boot menu &
launches automatically after 30 seconds.
I realized that everything in Windows 7 is installing under D:\etc. When I
remove Vista & revert to one larger partition what will happen to all the
installed programs that have a path to D:\? Won't the one drive become C:|?
When installing Windows 7, I deliberately created a partition at the front
of the drive & moved Vista to the 2nd partition assuming that whichever OS I
booted into, it would use C:\ as the letter for their individual partition.
Thanks,
Rich

Win7 installs its own bootloader, similar to but more robust than the Vista
bootloader.
You can go into Control Panel in Win7 and change the time out for booting to
the default OS to just a few seconds, so that you have time to hit the F8
key if needed on boot-up.
With Win7 as the default OS it does not matter what you do to the
partition/drive that has Vista on it. Win7 will always see itself on the D
drive. Most programs that have been installed will look for Windows on the D
drive so do not change the drive letters.
It has been many years since an OS had to be installed on the "C" drive.