It would help if you could supply exact messgaes and more detail in general.
It sounds like your computer could not locate the hard drive (or the boot record on a hard drive) with the original Vista install on it. In this case you want to run the repair option from the CD. Tutorial here: http://www.ocmodshop.com/ocmodshop.aspx?a=1372
Try that, it may make it unnecessary to reinstall at all.
Also make sure your Vista hard drive is still listed in the BIOS as the 'first' hard drive - if not make it so.
Like I said I was powering down my computer and as I was powering it down windows had an automatic update. Then it installed it and powered down. When I turned the computer back on it asked me to put in the boot disk (it was the same message when the computer first posts and asks for the vista/or OS disc).
I put in the Windows Vista disc and it was loading the finals and I got to the screen that asked if I wanted to upgrade or install. I could not even choose to upgrade I could only choose install. Then i clicked install and it said the memory for the harddrive did not match up.
So then... which I should not have done... messed around and unplugged the HD and plugged it back in and now it is giving me a "bootmgr is missing press alt ctrl del to restart"
So ya fun fun. So now my laptop AND desktop are not working