Dave - You are my hero of today - you saved me hours! thanks a lot!
I tried the substring method you pointed me to but at first it does not seem to change anything
Then I digged a little deeper into the "substring" xpath- functions because i wanted to understand what I am doing there.
I ended up with the following code (for the image part) that now works as I wanted it to (I already checked the display in the codesection and it does not translate the gt and lt items - so the code below should work for others too):
<img>
<xsl:attribute name="alt">
<xsl:value-of select="./P/NB_Store_ProductsInfo/ProductName" />
</xsl:attribute>
<xsl:attribute name="title">
<xsl:value-of select="./P/NB_Store_ProductsInfo/Summary" />
</xsl:attribute>
<xsl:attribute name="src">
<xsl:value-of select="substring-after(substring-before(./P/NB_Store_ProductsInfo/XMLData,'</txtcolorimage>'),'<txtcolorimage>')" />
<xsl:text>_</xsl:text>
<xsl:value-of select="substring-after(substring-before(./P/NB_Store_ProductsInfo/XMLData,'</txtcolordefault>'),'<txtcolordefault>')"/>
<xsl:text>.jpg</xsl:text>
</xsl:attribute>
</img>
Now the standard product Image for related Products is replaced by the one i define in the Product Details custom fields ...
regards and many thanks again for the fast and perfect support of dave and rob!
Gerald