I am trying to use the XSLT editor to create a filter and am having no luck, I have followed suggestions from previous posts as well as the  user manual, the olny thing that is different is that the field i am trying to filter is a true/false. I am including the code below any help would really be appreciated

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:udt="DotNetNuke/UserDefinedTable">
  <xsl:output method="xml" indent="yes" omit-xml-declaration="yes" />
  <!--
  This prefix is used to generate module specific query strings
  Each querystring or form value that starts with udt_{ModuleId}_param
  will be added as parameter starting with param
  -->
  <xsl:variable name="prefix_param">udt_<xsl:value-of select="//udt:Context/udt:ModuleId" />_param</xsl:variable>

  <xsl:template match="udt:Data" mode="list">
    <p class="normal">
      <xsl:call-template name="EditLink" />
      <br />
      <xsl:value-of select="udt:Company_x0020_Name" disable-output-escaping="yes" />
      <br />
      <xsl:value-of select="udt:Description" disable-output-escaping="yes" />
      <br />
      <xsl:value-of select="udt:Phone" disable-output-escaping="yes" />
      <br />
      <xsl:value-of select="udt:Web_x0020_SIte" disable-output-escaping="yes" />
      <br />
      <xsl:value-of select="udt:AmusementParks" disable-output-escaping="yes" />
      <br />
      <xsl:value-of select="udt:City" disable-output-escaping="yes" />
    </p>
  </xsl:template>

  <xsl:template match="/udt:UserDefinedTable">
    <xsl:variable name="currentData" select="udt:Data[udt:AmusementParks='true']" />
    <xsl:apply-templates select="$currentData" mode="list">
    </xsl:apply-templates>
  </xsl:template>

  <xsl:template name="EditLink">
    <xsl:if test="udt:EditLink">
      <a href="{udt:EditLink}">
        <img border="0" alt="edit" src="{//udt:Context/udt:ApplicationPath}/images/edit.gif" />
      </a>
    </xsl:if>
  </xsl:template>
</xsl:stylesheet>

udt;AmusementParks contains an image, either checked.gif or unchecked.gif. You want to query udt;AmusementParks_UDT_Original instead. Please refer the "Hidden Column Help" for more information.

Your Xsl is fine, I would place the filter exactly te same way.

Sebastian's Answer refers to the Grid rendering mode, that mode allows the definition of the filter inside manage udt. The filter would als use the hidden column and be defined as AmusementParks_UDT_Original='true' 

 <xsl:template match="/udt:UserDefinedTable">
    <xsl:variable name="currentData" select="udt:Data[udt:AmusementParks_UDT_Original='true']" />
    <xsl:apply-templates select="$currentData" mode="list">
    </xsl:apply-templates>
  </xsl:template>