I think you could use something like this as a starting point if you are using 6.3 or newer. This should show the waiting.gif once the search below starts, and it would show the chart once the search is done.
<html rejects="$show_panel$">
<img style="..." src="/static/app/<APP_NAME>/waiting.gif"/>
</html>
<chart depends="$show_panel$">
<search>
<query>...</query>
<progress>
<condition>
<unset token="show_panel"/>
</condition>
</progress>
<done>
<condition>
<set token="show_panel">true</set>
</condition>
</done>
</search>
</chart>
