"Frank Kabel" wrote...
download Morefunc.xll (http://longre.free.fr/english)<and have a look
at THREED for this purpose
....

Not exactly a complete answer. Using THREED, the formula would need to look
something like

=INDEX(THREED(alpha:omega!A1:B5),MATCH("x",THREED( alpha:omega!C1:C5),0),
{1,2})

But THREED isn't necessary. It's possible to use COUNTIF(INDIRECT(...)) to
determine the worksheet containing the first 'x'. If the worksheets to
search were listed in a range named WSList, the array formula

=INDEX(INDIRECT("'"&LOOKUP(2,
1/COUNTIF(INDIRECT("'"&WSList&"'!C1:C5"),"X"),WSList )&"'!A1:B5"),
MATCH("x",INDIRECT("'"&LOOKUP(2,
1/COUNTIF(INDIRECT("'"&WSList&"'!C1:C5"),"X"),WSList )&"'!C1:C5"),0),
{1,2})