Can you explain exactly how you did the transfer? Did you do an export from iPhoto or some other photo management software (this is what I'm guessing you did at this moment)? If you did do an export, you'll pretty much always end up with JPEGs instead of RAWs (of course, part of this also assumes you even had your camera set to store RAWs). To get the actual RAW photos (assuming once again that your camera was set for RAW and that's what you originally imported) - you will have to dig into the folder structure to locate the raws and manually copy them over to your storage medium.
Once you get into your Photo folder, find the storage package for the software you were using (ie: iPhoto) - you will then have to right click (or control click) on the package and show the contents (since usually double clicking on these storage packages will actually open the photo management software) and then you will have to search through to find the photos you want to copy. Unfortunately, I don't have my Mac in front of me atm to give you a full path example for where to look in an iPhoto library.
Thank you for your reply. Sorry this is my first contact with MAC systems and I don't know my way around.
Part of my problem is that although the pictures show as RAW in iPhoto they don't show in Finder, which I assume you mean by 'folder structure'. I have tried control click on iPhoto, but can not find the pictures listed.
Once in there, you should see an item called iPhoto Library
Right click (or control+click) on iPhoto Library and select Show Package Contents
A window should open up like a regular folder - in there should be a folder called Masters - double click on that.
RAW photos should be stored in there - you'll have to dig into the folder hierarchy to find your folders. Once you do, find the image files and copy them to your thumb drive / external HDD and copy to your windows machine