I finally found a way to get my sites containing flash, xhtml 1.0 validated! I have tried several different quirks and tricks to make the flash validated, with no real success - the Flash Satay example from an article posted at A list apart and the default Adobe embed to mention a few.
The solution was SWFObject from deconcept.com! To say it directly:
A little update
Robert Nyman has written another way to do this, have not tested it yet, but check it out.