Ad Peeps does not support alternative ads for flash ads
however, you could upload a GIF/JPG/PNG ad and it would be
shown in regular rotation along side the flash ad.
You could also turn on Ad Grouping in the HTML Generator so
that only one ad at a time would be selected.
With this approach, your flash enabled visitors would
sometimes see the regular ads, and also sometimes the flash.
For the visitors who don't support flash, they would ONLY
get the regular images.