Installing the bootloader for OS X will break Windows boot manager, you need to fix it if you want to keep using it. You need to use the same version Windows DVD you have installed or similar (i.e. you cant use XP disc to fix Seven boot manager, but you may be able to use Vista's maybe...).
I dont know what OS X distro or retail you are going to install, but you will need a bootloader to start it up, Windows boot manager will know nothing about OS X, it wont show up in msconfig or bcd, you need a third party tool like easybcd to add OS X bootloader to Windows boot menu or, alternatively, use Chameleon or PCEFI (most common OSX86 bootloaders/managers) to multiboot instead of Windows.
Also the partition created within Windows most likely wont be valid for OS X installation, you need to another partition manager like parted magic to create a HFS+ type partition without redoing your entire partition layout.

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AsRock P45TS | C2D E8200 | GeForce 8600GTS
Mac OS X Snow Leopard 10.6.1 + Windows 7 Ultimate 6.1.7600 + Fedora 11