a tooltip is what you get when you hover over a link or image - hover over the powered by link here to see it.
You can make the images yourself. Or ask in the images and style forum if someone will help you. I haven't seen any ones that are likely to match your colours recently!
Faizan, maybe you really really like the XP-look, but that doesn't mean XP-style icons make every forum look better. IMO they would look bad on Hayley's forums because of the colors that would clash. The pink and yellow folder icons she has now look right in place.
Also, the forum icon sets on my site are incomplete if you're going to use them on a version 3.4.xx of the forums. They were all created for version 3.3.xx and will not have some of the icons needed for a complete look on a 3.4.xx forum. At the bottom of the page you linked to are some links to other sites that also have forum icon sets. Those are newer and more likely to be of use.