css transitions

this is the way to go
https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Using_CSS_transitions

css easer
http://matthewlein.com/ceaser/

For me the best approach, though not the easiest, is using a sprite sheet and CSS transitions. This can make a very compact banner. Flash can export a sprite sheet with coordinates.

Works for position or opacity, and you can do some custom eases.