PNG transparency with IE6

Leo

I need to overlay two PNG images and see this in IE6.

Simple overlay like:

<div style="position: relative; width: 150px; height: 300px;">
<img src="im1.png" alt="" style="position: absolute; top: 0; left: 0;">
<img src="im2.png" alt="" style="position: absolute; top: 0; left: 0;">
</div>

works only for 256 color images, it doesn’t work at all ofr true color images.

Is there any way to overlay true color images in IE6?