I've been messing around in Photoshop to create a 1x1 semi-transparent image to use as a background on parts of my website. It has been successful to a degree. The transparency works in Firefox and Chrome, but fails miserably in IE, where the background is completely opaque. I think there's something I must not be doing right in PS. All I did was set the opacity on the layer to 30%. Should I be doing something more?

I know it has to work in IE, because this page works perfectly in IE.

SOLVED!
Adding a doctype tag in the source code somehow fixed it.