You are really great! At last i worked it out, and here's my "very very un-professional" code (i'm also new to it, hehe) for your reference.
<xsl:template match="entry">
<xsl:variable name="link" select="@href" />
<xsl:variable name="b" select="@b" />
<xsl:choose>
<xsl:when test='boolean($link)'>
<a href="{$link}">
<xsl:choose>
<xsl:when test='boolean($b)'>
<b><xsl:value-of select="."/></b>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="."/>
</xsl:otherwise>
</xsl:choose>
</a>
</xsl:when>
<xsl:otherwise>
<xsl:choose>
<xsl:when test='boolean($b)'>
<b><xsl:value-of select="."/></b>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="."/>
</xsl:otherwise>
</xsl:choose>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
<xsl:template match="entry">
<xsl:variable name="link" select="@href" />
<xsl:variable name="b" select="@b" />
<xsl:choose>
<xsl:when test='boolean($link)'>
<a href="{$link}">
<xsl:choose>
<xsl:when test='boolean($b)'>
<b><xsl:value-of select="."/></b>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="."/>
</xsl:otherwise>
</xsl:choose>
</a>
</xsl:when>
<xsl:otherwise>
<xsl:choose>
<xsl:when test='boolean($b)'>
<b><xsl:value-of select="."/></b>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="."/>
</xsl:otherwise>
</xsl:choose>
</xsl:otherwise>
</xsl:choose>
</xsl:template>