Hello... http://www.silverstonetek.com/techtalk_cont.php?tid=10055&area= it's all about finding the right size and mounting hole dimensions, when it comes to Dell, Gateway, Acer, etc... ATX is the defacto in availability with Custom cases and builders, but some brand names like to throw a wrench into the options of the Upgrader... get a ruler out and measure in MM 's, The outside and hole mountings, so we can be sure to give you good advice.
And post a picture too, is also very helpful.