Replacing strings

Hello,

i have a string that contains the value of CDATA field.

The string may contain following string:
"Vorbedinung"
"vorbedingung"
"VORBEDINGUNG"
and many, many other strings.

The strings should be replaced by "PRECONDITION".

I'm using following code up to now, but so i can replace just one string.

Does anybody know how to replace these strings?

Thanks
Sven

<xsl:template name="replace_precond">
	<xsl:param name="string" />
	<xsl:param name="from" select="'Vorbedingung'" />
	<xsl:param name="to" select="'PRECONDITION'" />
	<xsl:choose>
		<xsl:when test="contains($string, $from)">
			<xsl:value-of select="substring-before($string, $from)" />
			<xsl:copy-of select="$to" />
			<xsl:call-template name="replace_precond">
				<xsl:with-param name="string" select="substring-after($string,
$from)" />
				<xsl:with-param name="from" select="$from" />
				<xsl:with-param name="to" select="$to" />
			</xsl:call-template>
		</xsl:when>
		<xsl:otherwise>
			<xsl:value-of select="$string" />
		</xsl:otherwise>
	</xsl:choose>
</xsl:template>