Check this site, grab the function code, load up a 1px x 1px 8bit transparent spacer.png, and ref the function as instructed. VoilÃ ! IE with PNG-24 transparency!
It actually works. I remain amazed. You can check it by visiting P O V using IE.... I only have IE6 to test with now, but I understand it works for 5.5+.... (and yes, I'm aware that the 3px jog in the header is still showing - I just spent a day and a half getting transparency to work; I'll fix the 3px jog tomorrow!)