Viktor, thank you for the answer, my problem was solved. 

Hi Oamike,

I wrote for you sample which will do what you probably need. The only problem, is size on initialization maybe wrong because target url is not loaded yet. I used delay with 500ms, however, it can be not enough. You may try to enhance that initialization logic. Maybe add interval with checks if iframe is loaded, process onload within targetUrl and call adjustTab on main page, etc. Similar operations can be quite complex and not related to tab.

<script type="text/javascript">
function adjustTab(id, oWebTab, oTab)
{
 if(id)
 {
  oWebTab = igtab_getTabById(id);
  if(!oWebTab)
   return;
  oTab = oWebTab.getSelectedTab();
 }
 var cp = document.getElementById(oWebTab.ID + '_cp');
 var doc = oTab ? oTab.getTargetUrlDocument() : null;
 if(!doc || !cp)
  return;
 var body = doc.body;
 var width = body.offsetWidth, height = body.offsetHeight;
 cp.style.width = (width + 70) + 'px';
 cp.style.height = (height + 70) + 'px';
}
function UltraWebTab1_AfterSelectedTabChange(oWebTab, oTab, oEvent)
{
 adjustTab(null, oWebTab, oTab);
}
function UltraWebTab1_InitializeTabs(oWebTab)
{
 window.setTimeout('adjustTab("' + oWebTab.ID + '")', 500);
}
</script>
 <igtab:UltraWebTab ID="UltraWebTab1" runat="server">
  <ClientSideEvents AfterSelectedTabChange="UltraWebTab1_AfterSelectedTabChange" InitializeTabs="UltraWebTab1_InitializeTabs" />
  <Tabs>
   <igtab:Tab Text="New Tab">
    <ContentPane TargetUrl="Temp.aspx">
    </ContentPane>
   </igtab:Tab>
   <igtab:Tab Text="New Tab">
    <ContentPane TargetUrl="DialogUrl.aspx">
    </ContentPane>
   </igtab:Tab>
  </Tabs>
  </igtab:UltraWebTab>

Viktor

Is there a way to set the WebTab to auto-resize - based on the content of the current tab, and not the size of the window on the client?

Or is this method described above 'better'?

I'd prefer for my user's browser window to have the scroll bar, and not my tab control...

I am using a master page with the UltraWebTab - and TargetUrls for each ContentPane (all TargetUrls are pages I server from ASP.NET)