i always forget the syntax for mt templates using the <mt:for> tag.

mt_for_sample.html

<ul class="gallery"> 

   <mt:setvarblock name="num_assets"><$MTNumAssets$></mt:setvarblock>
   <mt:setvarblock name="num_assets"><mt:var name="num_assets" op="++"></mt:setvarblock>
   <!-- num assets = <mt:var name="num_assets"> -->

   <MTIfHasAsset placement="1">
      <!-- Has a numbered asset! -->
       <mt:for var="i" from="1" to="$num_assets" increment="1">
         <mt:AssetContainer placement="$i">
            <mt:SetVarBlock name="caption"><mt:AssetDescription encode_html="1"></mt:SetVarBlock>
		<mt:AssetProperty property="image_width" setvar="this_width">
		<li<mt:If name="i" eq="1"> class="active"</mt:If>>
			<img src="<mt:If name="this_width" gt="500"><mt:AssetThumbnailURL width="500"><mt:Else><mt:AssetURL></mt:If>" title="<mt:Var name="caption">" alt="<mt:Var name="caption">">
		</li> 
		   </mt:AssetContainer>   
	   </mt:for>
<MTElse>      
   <!-- Does not have a numbered asset! -->
   
   	<mt:EntryAssets tag="@gallery">
   <mt:SetVarBlock name="caption"><mt:AssetDescription encode_html="1"></mt:SetVarBlock>
   		<mt:AssetProperty property="image_width" setvar="this_width">
   		<li<mt:If name="__first__"> class="active"</mt:If>>
   			<img src="<mt:If name="this_width" gt="500"><mt:AssetThumbnailURL width="500"><mt:Else><mt:AssetURL></mt:If>" title="<mt:Var name="caption">" alt="<mt:Var name="caption">">
   		</li> 
   	</mt:EntryAssets>
   
</MTIfHasAsset>
</ul>