I have just upgraded my HD on my MacBook Pro A1226, on which I run bootcamp with win XP. Because this thread was so useful I thought I'd share a list of steps I (complete novice at this stuff) went through. Basically what Matthewfrey suggests works a treat but here is the step by step proceedure I went through to get into 500GB 7200 rpm bootcamp bliss:
1. Download carboncopy and winclone.
2. Install new HD into a SATA external enclosure.
3. Carbonccopy mac partition to external HD from within Mac of course.
4. Test boot from external HD (hold down option buttin at start etc.).
5. Intall new HD into laptop following ifixit guide.
7. Install old HD into external enclosure and attach to laptop.
8. From within Mac winclone windows partition and save the image onto new HD (my old one was full).
From here I fumbled around a bit and I'm sure there is a better way but the issue I had was that I mostly use windows because the software I spend most of the day using is specialist PC stuff so my partition is stronlgy biased to widows. The following steps can be optimised if you are not being a miser with your new HD partition like I am by having a minimum amount of space assigned to Mac (it's just a regrettable fact that I can't run the software I use for most of the working day in mac, and emulators are rubbish for these apps-and I have tried Parallels and Fusion. I live in hope that one day there will be a magic mac that means I can choose never to use windows again). As an aside; getting a mac was an experiment for me that I started two years ago. The aim was to get a reliable laptop. From that perspective is has been a great success, on the downside using Mac, from being brought up on PC, turned out to be a real pain because it made me realise how much of a slug windows is so that now I'm continually frustrated with it-windows that is.
So with this in mind:
9. Erased the Windows partition on the old HD and then move the winclone image from the new HD to the old one.
10. Using Bootcamp patition the new HD for windows.
11. Using Winclone, restore the windows image, which is now residing on the old HD, to the new bootcamp partition. Restoring the win image is time consuming so plan your day arouns it.
12. Make a couple of donations to the good people at Carboncopy and Winclone for making their available. Bob's your uncle and you're back in business.