Boot Manager

#1
I somehow uninstalled/deleted my boot manager on windows vista. I bought the netbook used and have no disk. I also have critical data on this machine that I can't afford to lose. I am a computer idiot so please explain things in simple terms so I can understand.

I hope you guys can help!! I took it to my local repair facility and they said they could only do a complete re0install and I would lose all my data!!

PLEASE HELP!