Vista expiration will not do anything to hurt your computer. It just won't
work any more.
I suspect that you might benefit from reading what the Customer Preview
Program for Vista is all about (from the CPP home page):
From
http://www.microsoft.com/windowsvista/getready/preview.mspx
"Note: This is beta code and should not be used in a production environment
or on a main machine in the home. Beta 2 is intended for developers, IT
professionals and technology experts to continue or begin their testing of
Windows Vista. Before you decide to use Beta 2, you should feel comfortable
with installing operating systems, updating drivers, and general PC
troubleshooting. Some risks of using beta operating systems include hardware
and software incompatibility and system instability. If you have concerns
about installing this beta software on your computer, we encourage you to
obtain the final release version of Windows Vista when it is available in
2007."
In other words, don't use Vista on your only day to day computer.