X-Cart/Smarty Custom PHP Scripts

[empiresolutions]

i have what may be a very simple question for someone who has worked with X-Cart or Smarty.

I am adding a rollover image next to the category names in the main navigation. The following is my stripped down for this post version.
[php]
{foreach from=$categories item=c}

<div>

<div><img name="{$c.category}_" src="{$ImagesDir}/custom/paw.gif"></div>
<div><a href="home.php?cat={$c.categoryid}">{$c.category}</a></div>

</div>

{/foreach}
[/php]I need to remove spaces in the names given at

name="{$c.category}_"

I want to make it

name="{str_replace(" ","_",$c.category)}_"

My attempts don't work and I get this error

Error: Smarty error: [in customer/categories.tpl line 26]: syntax error: unrecognized tag: str_replace(" ","_",$c.category) (Smarty_Compiler.class.php, line 436) in C:\apache2triad\htdocs\clients\sitename.com\www\Sm arty-2.6.12\Smarty.class.php on line 1095

My question is.. How can I make PHP functions work in X-Cart/Smarty?

I cant even find where $c.category is set. Thanks much.

[empiresolutions]

Thanks Jay. Here's the solution-

{$c.category|replace:" ":""}

im now finding that slashes are not allowed either.

{$c.category|replace:" ":""|replace:"/":""}

works too. sweet.