In case you need to display a transparent PNG in IE 5+, but you would also like to make it appear in other browsers as well, you can do so with a simple css trick using filters.
The essence of the trick is that you don't place the PNG image directly as an IMG tag into the HTML code (because in that case IE would display it improperly - with an ugly background colour), instead, define it as the background of a transparent GIF and add an Alpha filter with the opacity set to zero. This way it will be invisible in IE, but visible in all other browsers.
Now, in order to display the image in IE as well, all you need to do is sniggle it into the SPAN tag surrounding the IMG tag, with the help of the AlphaImageLoader filter.
Voilá! Just check out the source.
Note: if a hyperlink is added to the picture, IE will not display the cursor properly, even if you include "cursor:pointer; cursor: hand;" in the style definition of the A or the IMG tag. This is why there's another DIV tag around the picture and the hyperlink tag, with cursor definitions.
Note2: Active content must be allowed in the browser.