Animation in the background of the form on master page like moving clouds or water flowing

I've a requirement where I need to have animation in the background of the form on master page like moving clouds or water flowing.  I've no idea how to do this. I checked AjaxToolKit but didn't find anything for this requirement, unless I missed somehthing.  Any help with this is much appreciated. I am using  asp.net c# 3.5.
Thanks,
Rose :)