You could try on s/w tools like:
Vista Boot Pro
EasyBCD
oops.. no.. ur vista dvd will have an option to repair it... restart comp booting into vista dvd.. on the install screen, you will get an option to repair it.
btw, if you were on Hardy earlier, use its other feature where in you dont hafta create any ext3 partition.. install it as a s/w in vista, but still run on its own.. so then.. you would not have to worry about your boot record getting corrupted