Hi there!

Well, I use rollovers on my site, but I also have
an archaic habit of coding everything by hand, so
I'm afraid I'm totally clueless on Dreamweaver. 
:(  However, it sounds as if your rollover code
isn't pre-loading the images before the page is
shown, which can cause loading delays on
mouseover.  Feel free to take a look at the source
of any of my framing or thumbnail index pages for
samples of this extra bit of code -- it's right
near the front of the .html file.

Best of luck to you!  :)