Step 3 - Fix Boot Loader:
Vista will load the GUI files, and then display the loading splash screen.
-Click "Next" on the first screen
-Once the "Install Now" menu (do not click Install Now) choose "Repair Your Computer":
-You will be prompted to choose the OS to repair. Don't worry if Vista is the only OS that shows up, even after a search.
-I realize there is a "Fix Startup" option, but it's been my experience that it doesn't work, and this method will.
-choose to open a "Command Prompt":
type in the command prompt the following 2 lines (separatly):
-close the prompt and restart
-now that Vista controls your boot loader, the process is mostly finished, now we need to inform Vista that XP is installed, as
to enable the boot loader selection screen.
*There are programs such as VistaBootPRO that will do this for you, but it requires .NET framework, etc, so I did it the manual