From what I understand, it will be necessary to use completely re-boot your Mac in Windows in order to do some things that won't quite work with Parallels or Fusion, but personally, everything that I do can be done in Fusion from within OS X.
Either way you'll need to create the Windows partition with the Boot Camp Assistant in the applications menu. The assistant is pretty self-explanatory and easy to follow, but here's a tutorial:
Using Boot Camp to install Vista on your Mac: The Complete Walkthrough - Simple Help
After the partition is created and Windows is installed, you can either re-boot while holding down the Option key and you'll be presented with a choice of operating system, Mac OS X or Windows. To switch between OSes, you'll need to reboot and hold Option again, but if you buy a virtualization app, you can just start up Windows from within OS X.
I've never had a virtual machine on a Windows computer, so I don't know what to tell you about that.
It's tempting to wait until the latest version of the Macbook and Leopard are released, but there is ALWAYS a better version coming right around the corner. You'd be waiting forever to buy the ultimate, newest generation Mac. Wait for Snow Leopard if you want to, but remember that before school starts, you'll want to give yourself plenty of time to really get to know your Mac before you have to start using it all the time. If you have an issue or question, you won't want to have to put all your work on hold until you figure it out.