Three Answers :
Simple :
<img>
<xsl:attribute name="src">
<xsl:value-of select="//your/xquery/path"/>
<xsl:value-of select="'vmLogo.gif'"/>
</xsl:attribute>
</img>
Using 'concat' :
<img>
<xsl:attribute name="src">
<xsl:value-of select="concat(//your/xquery/path,'vmLogo.gif')"/>
</xsl:attribute>
</img>
Attribute shortcut as suggested by @TimC
<img src="{concat(//your/xquery/path,'vmLogo.gif')}" />