Buffmin, I would advise you that as designer you educate your client what’s good and bad practice in web design. Explain her that animated background images are counter productive because they are distracting from the actually relevant things on the site. Animations should be used very
sparsely and unobtrusively and special care should be taken as to when to use animations. It definitely shouldn’t be used just because one might casually think it’s funny and entertaining.
Giving your clients what they want is just half the job. The other half is to guide them and let them know that you
are the designer and you
know what should and shouldn’t be used for a successful professional website.
Now, that said: If you still want to have animation going on then you might wanna look into the emile animation framework
. It’s used on http://benefitcosmetics.com/
, for example.