Edit**
try this. make sure you use the <img src /> tag and that your files re in the skin1 images dir
<div class="HeadLine" style="text-align: left; height: 153px; width: 100%; margin: 10px 0px 0px 0px">
{if $main and $cat eq "110" }
<img src="{$ImagesDir}/IR_HdrImg.jpg" />
{elseif $main and $cat eq "120"}
<img src="{$ImagesDir}/textbanner.jpg />
{elseif $main and $cat eq "130"}
<img src="{$ImagesDir}/IR_HdrImg.jpg.jpg />
{else}
<img src="{$ImagesDir}/textbanner.jpg />
{/if}
</div>