At most, it will prepare your system for Windows 7 should you choose to upgrade in the future. Regardless of what you do, be sure to back up your files before installing any updates, or installing Windows 7.
You can do this by installing NTFS-3G and then cloning the Windows installation from the Mac side (the utility Win Clone is a good option for this), or you can do this by running a cloning program from within Windows.
Additionally, an upgrade can only be done for a version of Windows 7 that is the same "bitness" as the current operating system.
This means that you can only upgrade to a 32-bit version of Windows 7 if you have a 32-bit version of Windows Vista installed, and likewise for the 64-bit version.
(Apple provides a helpful list for that.) Assuming it does, you'll want to boot into OS X and make sure that you have any and all software updates installed.