If by "fix it" you mean uninstall Windows Vista and go back to Windows XP,
unfortunately the chances of successfully accomplishing this are not good. I
suggest reading the following thread:
http://neosmart.net/forums/index.php?gettopic=38&p=1
This is the only information I am aware of that deals with uninstalling
Windows Vista and going back to Windows XP after you have installed Windows
Vista over Windows XP.
Always remember that installing an operating system to the same partition
that another operating system is installed on is a non-reversable operation
that renders the previous operating system unbootable, probably for good.
The correct way of installing two operating systems on the same computer is
to install each operating system to its own partition.
Good luck.
- JB