Let's see if I can explain it.
I have a pictures gallery with thumnails, so you click on the thumnail and you get the large pic. My problem is that some pics are bigger than the screen. I've seen in some sites that when a pic is too big, it gets smaller (once it's loaded) and you can enlarge it clicking on a small icon on the lower right corner of the pic. How can I do this?
I'm not sure if you will understand what I mean...

it depends of which version of windows you're using. i think that only works on windows XP, not windows 200 or anything before that...

if I'm understanding you correctly, the picture should automatically do that if you are viewing it in a newer version of Internet Explorer- I believe it's the IE image toolbar that has the option to enlarge the image

That's what I thought, that IE does that automatically. I'm using the latests IE version and Windows XP, so I don't know why it's not working with my pics.