How did the cells get their yellow color?
If manually try this method.
In 2003 you can specify the Format color to look for under
Edit>Find>Options>Format>Format.
Select the color from the Patterns dialog and Find All.
In the found dialog box the first cell will be highlighted. Hold SHIFT key and
scroll down to bottom of dialog box and select last cell.
Those yellow cells will be highlighted.
If the cells are colored due to Conditional Fomatting either select by condition
or by code.
See Chip Pearson's site for working with CF cells.
http://www.cpearson.com/excel/CFColors.htm
Also see Chip's site for working with colors, summing, counting etc.
http://www.cpearson.com/excel/colors.htm
Gord Dibben MS Excel MVP