You can transfer the license for CS4 to Mac (Crossgrade). Since I have always had both PC and Mac versions I've never done it, but I have read here that it's pretty painless (not a lot of time and money).
You'll have to contact Adobe Support directly: http://www.adobe.com/support/contact/
This is a User-to-User forum, but I'm guessing your best bet would be to cross-grade your version of PS CS4 for Windows to Mac.
The previous posts suggest a CS4 to Mac crossgrade but that means that you will lose your CS4 for Windows as the software can only be licensed to one platform or the other. This may be a problem if you still want to use Photoshop on your Windows computer.
You may also ask Adobe customer service about crossgrading/upgrading your spare license of CS2 to Mac. (Or you could crossgrade CS4 and use the CS2 license on your Windows computer)
Seeing the number of issues with Snow Leopard, you may want to install Windows on your MacBook to run your Windows version of Photoshop.
Yeah, I was wondering if he wanted to keep the Windows version active also, but I figured he'd run into the options available upon contacting Adobe, which he will have to do regardless...
The education license can be upgraded and crossgraded if there are any restrictions for the education version that will probably so for the upgrade, though i m not certain. You do have to contact Adobe sign an agreement that yo will destroy the original copy and you get the mac upgrade.
However you might need to work with adobe about the licensing since you will not have a Mac serial number for the previous version.
A little tricky also be aware you will not be bale to use the prior version on the Mac since the crossgrade disks do not exist.
Not like when you say buy CS3 and then upgrade to CS 4 all on the Mac you can install both versions, you will not be able to do this in this circumstance.