Sim, o Windows 7 quebrará seu GRUB. Você pode recuperá-lo assim:
1) Boot off the LiveCD
2) Open a Terminal and type in the following commands, noting that the first command will put you into the grub “prompt”, and the next 3 commands will be executed there. Also note that hd0,0 implies the first hard drive and the first partition on that drive, which is where you probably installed grub to during installation. If not, then adjust accordingly.
sudo grub > root (hd0,0) > setup (hd0) > quit
Reboot (removing the livecd), and your boot menu should be back.
Verifique O guia do How-To Geek para mais detalhes, caso você não veja o Windows no menu de inicialização após essa configuração.