No problem.. Follow these steps (Done in Office 2007, not sure which format you have)
- Select all cells in both columns
- Navigate to conditional formatting on the home tab
- Select highlight cells rule
- Select Equal to..
- In the first field put yes, and in the second field select yellow highlight
(You may have to go to custom highlight and then modify it yourself since it might not be a default setting in your ofice)
After that all your cells with YES in them will be highlighted in yellow.
If you have any troubles or any other questions, let me know.