We are not a dual boot support channel.
There is a #dualboot channel to provide support for this on Freenode. Please help them grow if you are interested in still doing this.
Multi-boot systems are a relic of the 90's when hardware was expensive and virtualization was non-existent or expensive. These days there is a wealth of free client based virtualization options.
Oracle Virtual Box (channel #vbox)
VMware Player (channel #VMware)
At one time you could find support forums all over the Internet on setting up multi-boot systems. Those days are gone and much of what you find now is outdated or inaccurate. Finding people who are both advocates and willing to help support/troubleshoot boot issues when things go wrong is also problematic. There are many who will argue for the viability and 'reasons' to do so, but most of them disappear or go silent when asked to help.
All the above said, here are some considerations BEFORE YOU TRY THIS.
Don't practice on your only/main/parents computer
Have RECOVERY MEDIA PREPARED and know how to use it. (You should have this already, but don't experiment without being able to start from scratch)
Have backups of your data. (Again, you should already have this but don't hand wave it off with hopes)
Reconsider - knowing your way around virtualization is a valuable skill
If you have read all the above and intend to continue anyway, here are some links for you to check out:
To understand how Vista/7 boot, see the BCD paper
Questions tagged 'multi-boot' at Superuser.com
Deleted my Linux partition. Now I cannot boot Windows. How to fix?
This boot information script (run from Linux) can be helpful in troubleshooting boot failure situations involving GRUB.
Dualboot issues (older XP/Linux info)