Hope you don’t mind me asking, but if you don’t have any objection to using CSS to manage the rollovers, why wouldn’t you use it?
There is no reason, in my view, to use Javascript to create mouseovers unless you wanted to use a library like jQuery or mootools to add some fancy effects to the rollover as well. CSS is far more efficient, and also means that you can use a single image with sprites… instead of retrieving a new image every time you want to do a rollover or having to use more code just to preload images.
(And that’s without mentioning the complete impenetrability of the MM_* functions built into Dreamweaver.)
