I've not used the GAG boot manager, but strongly suspect that you can rid yourself of it by opening up a command prompt on the Vista box, and using "fdisk /mbr". This should restore you to "Vista Only" boots if that is what you are after.
I assume that this removal of GAG is related to a removal of a Linux distro as well. What distro, and why are you reverting to using only Windows? Just curious.
Best of luck.