I am trying to create a table structure using XSLT where 2 rows are merged together for first column and for next column they are seperate. Something like
  ________
 | | |
 | |---|
 |___|___|

How can I achieve this?

You'd better provide an example with XML source, desired output and what you have done up until now with your XSLT. It'll be easier to help you if you help us help you...

I'm trying sth like
<fo:table-cell border-style="thin"
number-rows-spanned="2" number-columns-spanned="2">
inside <fo::table-row> to generate
a table where first 2 rows are merged

...
</xsl:when>
                <xsl:when test="../@refer_condition1='true' and ../@condition='^'
                            and ../@refer_condition2='true' and ../@condition2='^'">
                    <fo:table-cell border-style="thin"
                        number-columns-spanned="2" number-rows-spanned="2">                         <xsl:for-each select="parent::node()">
                        <fo:block start-indent="0pt" font-family="Arial"
                            language="EN-US" space-before="3pt"
                            space-before.conditionality="retain" space-after="3pt"
                            space-after.conditionality="retain" font-size="9pt"
                            font-style="italic">
                                <xsl:variable name="cond" select="preceding-sibling::node()/@condition"/>
                                <xsl:value-of select="$cond"/>
                        </fo:block>
                        </xsl:for-each>
                    </fo:table-cell>
                    <fo:table-cell border-style="thin"
                        number-columns-spanned="1">
                        <fo:block start-indent="0pt" font-family="Arial"
                            language="EN-US" space-before="3pt"
                            space-before.conditionality="retain" space-after="3pt"
                            space-after.conditionality="retain" font-size="9pt"
                            font-style="italic">
                            <xsl:for-each select="parent::node()">
                                <xsl:variable name="cond" select="preceding-sibling::node()/@condition2"/>
                                <xsl:value-of select="$cond"/>
                            </xsl:for-each>
                        </fo:block>
                    </fo:table-cell>
                </xsl:when>
...

I think that your problem isn't XSLT but XSL-FO... Try to post this in an XSL-FO forum... And make a simple example while you're at it...

Dijkstra's law on Programming and Inertia:

If you don't know what your program is supposed to do, don't try to write it.