Comparison of image file types (jpg, gif, emf)

Can someone point me to a good website that teaches the pros and cons of various different image file types, such as .jpg, .gif, .png, and especially Enhanced Metafiles? In my work I use Word a lot to edit documents with lots of pictures in and it's getting to the point where it would be good for me to learn when to use which file type when inserting images and why.

Thanks in advance...

Thanks for the link Jilariz. I'd have upvoted you for that link had you not posted that faggoty jif bullshit!