I read some posts, and found the best way to make a compatible css-file for both IE 6+7 and Firefox.Safari and Firefox on OSX reacts (almost) similar to Firefox on Windows.

It’s quite simple, and I’ve corrected IE 6 optimized sites in a matter of minutes.

This is the trick:

margin: 10px;
.margin: 10px; /* read by both IE 6 and 7 */
_margin: 10px; /* read by IE 6 only */

That’s basically it.

NOTE: Not W3C compliant stylesheet, but it will look great