Dreamweaver has full details in its help files.
Search for rollover since that's what Dreamweaver knows mouseover effects as.
You can use text and/or images and Dreamweaver will generate the code for you if you supply the necessary details.
Now that I've got that off my chest, try these sites to begin with:
They have a lot of ready to download 'copy and paste' code for menus (among other things).
Beyond that you might want to look at a third party program for generating menus. I'm quite impressed with Sothink DHTML Menu Builder click here
There are other alternatives out there but the above should at least get you going. Just make sure that you test yout finished site in older browsers (Opera, NetScape and Internet Explorer) to make sure everything works properly.