Get file verification error message after upgrade from ME to Win 2000

I just upgraded my HP Pavilion XT868 from Win ME to Win
2000. I now get an error that pops up saying to insert
Win 2000 CD because files have been found to be of the
wrong version. When I insert the cd nothing happens the
error does go away until I try to do something else then
it comes right back. How can I get rid of this error...

I was going to reinstall win 2000 but when I run the setup
it gives me a different error that another program has
only been partially installed and that I should quit win
2000 setup, log off my computer and log back on. It says
that a program will start automatically when I log back on
and that I should let it run until it finishes. But when
I log back on no program starts and I still get the same
error when I try to reinstall win 2000. Help please.