filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='image.png', sizingMethod='crop');

The above code will work for inline CSS, that is, CSS mixed with HTML:

<div id="png_bg" style="position:absolute; left:140px; height:400; width:400;
     filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(
     src='image.png', sizingMethod='crop');" >
</div>

If you don’t want to mix your CSS with your HTML, external style sheets are the obvious choice. However the above example won’t work in an external style sheet. Instead, the path to image.png needs to be absolute, like this: /direct/path/to/image.png

Your external style sheet would look something like this:

#png_bg {
    background-image: none;
    filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(enabled=true, sizingMethod=crop, src='/path/to/image.png');
}

Shout at me if I got this all wrong.

Assuming you want to disable a few select options, don’t try the following in IE6:

<select name="ie_sucks">
   <option disabled="disabled">One</option>
   <option disabled="disabled">Two</option>
   <option>Three</option>
</select>

Although the above example is valid XHTML (and therefore works in Opera, Firefox, Safari, etc), IE6 displays all three options as selectable, as if the disabled option was never set. Thankfully lattimore.id.au has come up with a nice fix.

Puke you later IE.

Update: I should also note that IE7 doesn’t accept disabled="disabled" in an option field. Sweet Christ.