Hi all

Many many thanks to Nick, as he pointed me into the right direction with the example he provided.
So, what is the scenario:

in Ant:
- I use MSBuild to build my solution files (and underlying visual studio project files)
- I create an XML build log using a MSBuild extension pack (found at http://msbuildextensionpack.codeplex.com/; see also http://www.msbuildextensionpack.com/help/4.0.5.0/html/242ab4fd-c2e2-f6aa-325b-7588725aed24.htm)
- translate the xml logging (using ant xslt statement)
- publish the translated xml via the jdtCompileLogPublisher

The translation sheet I used (probably not perfect XLST, but at least it works for the tests I performed):

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes" encoding="UTF-8" version="1.0"/>

<xsl:strip-space elements="*"/>
 
<xsl:template match="/build">   
    <xsl:text>&#10;</xsl:text>
    <compiler>
        <sources>
                <xsl:apply-templates select="//project" />
        </sources>
    </compiler>
</xsl:template>

<xsl:template match="project">
    <xsl:if test="substring(@file, string-length(@file) - 8) != '.metaproj' and substring(@file, string-length(@file) - 3) != '.sln'">
   <source package="{@file}" path="{@file}">
       <problems>
      <xsl:apply-templates/>
     </problems>
   </source>
  </xsl:if>
</xsl:template>

<!-- skip all the message lines in the original output -->
<xsl:template match="message">
    <xsl:apply-templates/>
</xsl:template>

<!-- handle warnings -->
<xsl:template match="warning">
    <problem id="{@code}" line="{@line}" severity="WARNING">
        <xsl:variable name="TheMessageContent">
            <xsl:value-of disable-output-escaping="yes" select="."/>
        </xsl:variable>
        <message value="reports warning {@code}: {$TheMessageContent}"/>   
        <source_context value="{@file}"/>
        <xsl:apply-templates/>
    </problem>
</xsl:template>

<!-- handle errors -->
<xsl:template match="error">       
    <problem id="{@code}" line="{@line}" severity="ERROR">
        <xsl:variable name="TheMessageContent">
            <xsl:value-of disable-output-escaping="yes" select="."/>
        </xsl:variable>
        <message value="reports error {@code}: {$TheMessageContent}"/>   
        <source_context value="{@file}"/>
        <xsl:apply-templates/>
    </problem>               
 </xsl:template>

</xsl:stylesheet>           

(hmm, looks the forum editor screws up the layout a bit :( )
Hopefully others can use this too.
For me, it shows now clearly the amount of error / warnings per visual studio project file, and the number of compiler warnings can be shown using the appropriate widget.

Once again, thanks  2 all for your support and pointing me in the right direction.

Regards, Pascal