So, lets see if I get this right.
You initially installed BC to 'c:\\programs', right? (Nothing wrong with that btw, especially on Vista)
And now the game won't install? So the installer says that the game is already installed, right?
In that case, uninstall the game through the Control Panel (Add/Remove Software). It will say that the program isn't instaled anymore and will ask if it can remove the reference. Choose to do so.
Now you ought to be able to install the game again.