This is actually very easy and doenst need 10 skins or 10 css files as salaro suggested
this solution is for ascx skinning, so you need to edit the ascx, not the html
<div id="tab<%=request.querystring("tabid")%>
your skin
</div
then in the css
#tab1 div.header {background-image:url(bg1.jpg);}
#tab15 div.header {background-image:url(bg15.jpg);}
All you need to do is give a wrapper around your skin a unique id and then in css you can style anything within this page
Have fun :)
so you give