Upgrading A Hard Drive

I have an older Compaq notebook that has a 80GB HD. I bought a 250GB HD to install on it. I had heard that the easiest way to do this was to install the new HD and do a clean installation of the OS (in this case Vista) I’d never done this before so I “practiced” on the old drive and it was fine. I installed the new drive and tried again and all I got was “system error, contact HP service” What am I doing wrong?