If you're going to run Windows in Parallels, go with at least 2 GB. I believe the MBP can take up to 3, right? You might even consider that, but probably not unless you find from experience that 2 is inadequate.
My Macbook has 2 GB and I wish it could take more (original CD model). When I run my Windows XP virtual machine in Parallels, nearly all of my memory is used up, and the entire machine slows to a crawl if I have too many other things open. The virtual machine is configured to run with 512 MB. Trying to run multiple virtual machines at once is just asking for pain.
That said, if you'll only be using Windows with Bootcamp, you may very well be fine with 1 GB. Though personally I view rebooting as incredibly inconvenient and to be avoided at all costs, so I strongly prefer the convenience of having both OS X and Windows at the same time with Parallels. But that's just me. 😉
