Images

You're definitely going to want to down size it in something like Photoshop.

If you want to keep the quality the try.

.image_class{
width: the_size_you_want;
height: the_size_you_want-too;
}

Hope that helps.

And to maintain proportions do something like this:

.image_class {
    width: 300px;
    height: auto;
}

You can scale your image by changing the value in the width property. The height property will make sure that your image's proportions are maintained. This is explained in greater detail as you go on. I'm fairly certain the Smells Like Bakin' project touches on this, so keep an eye out for that as it'll be specific to the setup.

Photoshop? Their is also a billion other ways to resize it with scripts but I personally like resizing and compressing the original most; to save on bandwidth/load-time.