newbie to XSLT, please help?

[musman007]

I have a requirement to convert following xml into another xml with correct values.. This is sample requirement
<MAINTABLE>
<TABLE1>
<ROW1>
<COL1>VAL111
</COL1>
<COL2>VAL112
</COL2>
<COL3>VAL113
</COL3>
</ROW1>
<ROW2>
<COL1>VAL121
</COL1>
<COL2>VAL122
</COL2>
<COL3>VAL123
</COL3>
</ROW2>
</TABLE1>

<TABLE2>
<ROW1>
<COL1>VAL211
</COL1>
<COL2>VAL212
</COL2>
<COL3>VAL213
</COL3>
</ROW1>
<ROW2>
<COL1>VAL221
</COL1>
<COL2>VAL222
</COL2>
<COL3>VAL223
</COL3>
</ROW2>
</TABLE2>
</MAINTABLE>

Number of tables are known but Rows and Columns are not. The requirement is that XSLT should be to render Table3. with same number of columns and rows. Only those rows and columns should be updated in table 2. otherwise all the data of table2 should be copied in table3. Please help