It's (almost) alsways better to use

	  <xsl:with-param name="StringToTransform" select="

rather than

	  <xsl:with-param name="StringToTransform">
		     <xsl:value-of
select="

but otherwise the code fragment that you posted looked Ok and would
replace " by "" if executed.

> But the double quotes are not getting replaced with double double
> quotes
so presumably the part of the stylesheet that you didn't show never
executes the part that you did show.

David