In cell A1, array enter (enter using Ctrl-Shift-Enter) the formula
=INDEX(ProductSelector!$I:$I,SMALL(IF(ProductSelector!$R$12:$R$100="X",ROW(ProductSelector!$R$12:$R$100)),ROWS(B$1:B1)))
and copy down.
You can hide the error values by using this slightly more complicated version:
=IF(COUNTIF(ProductSelector!R:R,"X")>=ROWS($B$1:B1),INDEX(ProductSelector!$I:$I,
SMALL(IF(ProductSelector!$R$12:$R$100="X",ROW(ProductSelector!$R$12:$R$100)),ROWS(B$1:B1))),"")
HTH,
Bernie
MS Excel MVP