re:
Ok a few questions:
1. What OS do you intend to install on the second partition?
2. I'd recommend booting into windows 7 and reallocating the partitions prior to doing the install of the New OS. That will save any drama's you may face.
3. If you're intending on installing a linux distribution, you'll need a 3rd partition with a size of about 3 - 5 Gb as a swap partition. The 2nd partition will be used for the linux file system i.e... ext2,3 or 4 *what ever one you decide to use*.
If you install Linux after Windows, then the new boot loader when you load your PC will be GRUB. If you did it in reverse cycle i.e... Linux then Win 7, you'll find that the boot loader will naturally use the Windows Default one.
If you're looking at installing an older windows OS as the secondary one, ensure the installation disk that you're using, has the hard drive sata drivers slip streamed on to it, especially if your PC has new hardware. You'll find if the hardwares new and the OS is old that you will more than likely not see your hard-drive and won't be able to install.