That is not easy, but possible. XSL doesn't include any date time functions, they are treated as strings, they look like 2005-12-31T23:59:55.0000000+01:00. You will have a chance if your month colum is a string with length 2 with content like "01", "02".

<xsl:variable name="currentMonth" select="substring( /udt:UserDefinedTable/udt:Context/udt:Now, 6, 2)" />

...

<xsl:foreach select="/udt:UserDefinedTable/udt:Data[udt:Month=$currentMonth]>

here is what i came up with 
My filed in the table was a text filed with the name of the month so i did the following

<xsl:variable name="monthnum" select="substring( /udt:UserDefinedTable/udt:Context/udt:Now, 6, 2)" />
     <xsl:variable name="currentMonth">
       <xsl:choose>
         <xsl:when test='$monthnum=01'>January</xsl:when>
         <xsl:when test='$monthnum=02'>February</xsl:when>
         <xsl:when test='$monthnum=03'>March</xsl:when>
         <xsl:when test='$monthnum=04'>April</xsl:when>
         <xsl:when test='$monthnum=05'>May</xsl:when>
         <xsl:when test='$monthnum=06'>June</xsl:when>
         <xsl:when test='$monthnum=07'>July</xsl:when>
         <xsl:when test='$monthnum=08'>August</xsl:when>
         <xsl:when test='$monthnum=09'>September</xsl:when>
         <xsl:when test='$monthnum=10'>October</xsl:when>
         <xsl:when test='$monthnum=11'>November</xsl:when>
         <xsl:when test='$monthnum=12'>December</xsl:when>
         <xsl:otherwise>none</xsl:otherwise>
       </xsl:choose>
     </xsl:variable>
    
  <xsl:foreach select="/udt:UserDefinedTable/udt:Data[udt:Month=$currentMonth]>

Thanks for your help