Some times you will run into an old application, or a poorly written new application, that expects your system drive to be 'c:/'.  This isn't normally an issue as most default installs have 'c:/' as the system drive, but...  As a technician I run into the odd oddball. 

Now, you could just change the drive letters, there is a good reg hack for that, and it's pretty straightforward, but...  There may be an easier way.

There is a command line program that will associate a path with a drive letter: subst

what you do is associate the root directory of your system drive to 'c:/', like so:

subst c: i:\

Then install the application.

There is one caveat. When the application asks you where you'd like to install the application, DON'T install it on the newly created 'c:/' drive.