Several web articles deal with using CSS Sprites.
This technique reduces the number of separate image fetches, each using an http request to the server, by combining (say) the icons, the small icons and navigation images into a single image file then using CSS positioning.
http://website-performance.org/
http://spritegen.website-performance.org/section/what-are-css-sprites/
http://www.alistapart.com/articles/sprites
Benefits are
less http connections ... therefore more connections available for simulataneously downloading something else, eg page specific media items.
faster download ... reduced wastage of space in network packets
better user experience ... no images popping up one at a time in the icon bar. They all get displayed in one hit.
Mark