That is the challenge to all skin sites presently. SKin sites have to be careful not to violate the 250K rule.

That is, if the average downloadable item of your site is over 250K (roughly) then you will not be able to pay for your site via banner ads.

The figure can actually be a lot lower but assuming your site becomes very popular, the 150K rule of thumb comes into play.

That's one of the killer things about msstyles, they average something like 600K per download, over twice the limit. Hence any site that has that as its main attraction is going to lose money if it relies on banners to pay for it.

That's why those theme sites out there that have tons of banner ads and pop ups have the same sections: WinAmp, ICQPlus, Wallpapers, Hotbars. They've gotten it down to a science. (example http://www.ezthemes.com/ )