You are confusing what boot camp or parallels do.
If all you want is the occasional use of Windows, and don't care if it runs a bit slower, then Parallels is a great way to go. You load Parallels and then it does all the work to install Windows. It does not create a separate partition, it keeps everything on the Mac OSX disk.
The downside of the Parallels first and no boot camp approach is that if you decide you want to go to boot camp, it's not trivial to move everything.
If you do a boot camp partition - the way you can boot to Windows and run it without OSX - it takes more time and effort on your part. The instructions must be followed exactly if you want it to work (and to ensure you don't do something dumb to destroy your OSX install. If youy can print out directions and follow them, it will be fine. After you get Windows up and running via boot camp, you can easily install Parallels and tell it to use your boot camp install. You then have the option of running Windows natively (booting to it) or running it by simply opening a Parallels VM from in OSX. Windows runs faster natively than in a VM. My gut is about 25% slower in the VM, but I've done no real tests.
I run using Parallels on occasion (now on V7 but started with V3 years ago) but most often I find I boot to Windows and run it via boot camp. If you do run via boot camp, you'll want to consider adding Tuxera NTFS to allow OSX to write to your Windows (NTFS) formatted disk and something like MacDrive to allow Windows to read/write to your OSX (HFS+) disk. With Parallels (no boot camp), you don't need either of these as it takes care of it for you.