Vista Installation incomplete...died halfway through installation

Ok, so Ive been trying to install vista for a while now, starting with the
betas and RCs. I gave up on them, but finally go the full, real version. I
tried installing vista, but its not booting. I think it got stuck halfway
through installation (at the part where it restarts?). Apparantly there seems
to be an old bootloader, and it thinks that the installation completed. Well,
now I cannot roll back and cannot complete the installation. Why cant vista
upgrade properly? What can i do to fix the problem? can i manually install
the missing files? (for example it says winload.exe is mssing). Grr.......