With VISTA as your current OS I believe you have the tools you need to do this with your existing drive, within limits. First step I suggest it to run the Defragmentation tool on your drive. Then look in Disk Management for how to Shrink your existing C: drive (Partition), thus creating some Unallocated Space at the end of your existing HDD unit.
Once that is done, you should be able to run Win 7 Install and be sure to install to the empty Unallocated Space, and NOT to the existing C: drive. This will create a new Partition out of that Unallocated Space and install to that new "drive".
Alternatively, of course, you could buy a new second HDD unit and run Win 7 Install to install on it, completely staying away from the Vista already on the C: drive. This actually might be neater and certainly would add to your storage space, but also add cost.
In either route, what should happen is that the Install process picks up the fact that another earlier Windows (Vista 64) already exists on the machine and will continue to exist. Then it will create a dual-boot option for you with a menu that comes up every time you boot to ask which OS you want to use this time. And in either route, the creation of the Partition and formatting of it will be done for you as early stages of the overall Install process - you don't need to do them "by hand" ahead of time. You just need to have a HDD unit with a chunk of empty Unallocated Space that can be used for this.
I am glad to here that Vista has some of these tools already on the drive and I may be able to do this without losing all my information.
I have decided to buy the windows 7 32 OS, and another 320Gig hard drive(which I tried to cancel from New egg, but got denied even though I cancelled within a couple minutes of placing my order). Oh well, I guess ill have 600 gigs of free space instead of 300.
Its not all that bad though, since with a different OS on each drive, If one of my hard drives crashes, I will always have a backup OS to go into to help fix the problem. And might be better in the long run.