I would do some research on it. I remember the XP days when Vista came out and the boot managers were different so I had to modify it to get it to work and I found instructions online how to do it. Your issue will be easier since boot OS's use the newer boot manager. It sounds like now your boot manager only knows about 1 OS and you will have to configure it. After its configured a menu will come up and you have to select which OS you want to boot int. It will set one as the default and if you don't select which OS it will automatically boot to the default.
I currently have Windows 7 64 bit installed in two partiions:
C: drive and E drive.
Everytime I start, windows from the C: partition automatically boots. How do I get the Windows from E drive to boot? Ultimately I'd like to use the windows from E drive (which has all my installed software) and delete the one from C: drive. The problem is that I installed the one on C: drive most recently. (Long story short, I tried to delete and old version of windows unsuccessfully, and had to unmount and reformat the partition.)
When I go to System Configuration under the Boot tab, I only see Windows in one partition (C: drive), so it won't allow me to delete that.