> How do I mark up a simple *and*?

use and.

    <xsl:when test="Image"> <!-- I need an "and
                                 NegNumber" test here -->
    <xsl:when test="Image and NegNumber">

although I suspect you don't need your tests at all as
it appears that what you want is
<Graphic>
 <xsl:for-each select="URL|Image|NegNumber">
  <xsl:attribute name="{name()}" select="."/>
 </xsl:for-each>
 <xsl:apply-templates select="Caption"/>
</Graphic>

(untested)

David


 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list