Everyone who has given a shot at designing a webpage probably knows this; IE6 (and older IEs) don't play well with PNGs; not when it comes to transparent PNGs at least.
Even though the new IE 7 supports PNG transprency, that is not the end of our troubles, there still lots of people using IE6.
I have discovered (not really me, but I don't remember where I have actually found it) that using the following in you IE css
can help you overcome the IEs problem with PNG transparency.
You should use it within conditional IE statements so only IE will read it and do one more CSS trick so that IE does not see the regular background CSS rule.
Take a look at a test page that I have prepared. Resize your browser to see that it actually does work as intended.
I meant to put the few lines of code that make a difference here but I can't make wordpress display them correctly, so you have to dig in the source of the test page yourselves (look at the last 10 lines before the closing of the head tag).
I have tested this with IE5.5 and IE6 and IE7 and FF2 and it works OK. I would be glad to hear in other browsers that does or does not work.
Unfortunatelly it does not work with IE5 (and so do all other similar solutions), since AlphaImageLoader was first included in IE 5.5.