Correct way to use images?

Hi, I’m new to WP but I think it’s great. My site is coming along, but I need to address the problem of images. On other CMS’s I’ve used, there were fields specifically for images of different sizes. So a post would have a thumbnail, a medium sized image and a full sized image. On the one hand limiting, on the other very simple.

On the current site I’m working on it’s basically the same deal. A post on the homepage will have either a thumb, a small, or a medium image depending on the category. When you go to the post, it should have its large image.

I’ve been faking it so far by putting the not-large image in the post, followed by <!–more–>, but now I need to code this correctly.

So what’s the proper method for adding and managing images in WordPress?

Thanks!