Maybe newbie...

<xsl:template match="alarmhistory">
<table border="1" cellspacing="0" cellpadding="3">
<tr>
<th bgcolor="#6699CC"><font color="#FFFFFF">D?but</font></th>
<th bgcolor="#6699CC"><font color="#FFFFFF">Fin</font></th>
<th bgcolor="#6699CC"><font color="#FFFFFF">Quantit?</font></th>
<th bgcolor="#6699CC"><font color="#FFFFFF">Type de probl?me</font></th>
</tr>
<xsl:for-each select="alarm">
<xsl:for-each select="problemtype">
<tr>
<xsl:choose>
<xsl:when test="position()=1">
<td><xsl:value-of select="../@start" /></td>
<td><xsl:value-of select="../@end" /></td>
</xsl:when>
<xsl:otherwise>
<td></td><td></td>
</xsl:otherwise>
</xsl:choose>
<td><xsl:value-of select="@qty" /></td>
<td><xsl:value-of select="@type" /></td>
</tr>
</xsl:for-each>
</xsl:for-each>
</table>
</xsl:template>

Which, when applied to the following part of a document:
<alarmhistory>
<alarm start="2002-01-01" end="2002-02-01">
<problemtype qty="3" type="10"/>
<problemtype qty="4" type="6"/>
</alarm>
<alarm start="2002-03-01" end="2002-04-01">
<problemtype qty="1" type="3"/>
<problemtype qty="2" type="4"/>
</alarm>
</alarmhistory>