And for Vista users:
How to resize photos in Vista
There are many applications that you can use to reduce the size of photos you take at high resolution. Another way, that doesn't require you to install third party software, is to use Windows Photo Gallery in Vista. It lets you set the picture size at 640 x 480, 800 x 600, 1024 x 768, 1280 x 1024 or the original size when you click the "Email" button (and it tells you the estimated file size in KB or MB for each resolution). And you don't actually have to send the photo to take advantage of this resizing ability; you can go through the process and then, when the mail message window opens with the resized photo attached, you can just drag it onto the desktop.