If you have the disc version, you just use the mac discs to install PSE 10 on your mac. Upgrading is the same no matter which platform you have--you'll have to buy the new version. You could just get the upgrade version, but over the next few weeks you're likely to see the full version priced much cheaper than the upgrade. If you're in the US, I believe that right now Costco has a very good price on it.
As for moving your catalog and photos: make a full backup in the windows version, then restore it to your mac. If you don't plan to upgrade the windows computer, you can restore a PSE 10 catalog to PSE 11 cross platform.