well from what I can gather and i can't test this because my only vista machine is at work is that you can simply go to start > run and type in bcdedit.exe or if that file is loaded or present during the installation process and you can drop to a command prompt you should be able to run it from there.
Another option would be to load a boot loader from a third party, but lets not go there yet.
As for the locking up, it probably didn't actually lock the installer was probably scanning your HD and your previous OS for upgrade options. The vista installer is not that fast, in fact I would go ahead and call it slow.