Try this:
- Define a character style to use as a highlight
- Open the Find and replace dialogue (Ctrl+H) and go to the Replace tab
- Put your search term in the Find what and the Replace with boxes
- With the cursor in the Replace with box, select Format > Style from the pull-down in the Replace group
- Select your new character style from the list and click [OK]
- Click [Replace All]
This works a) for me; b) with Word 2010
YMMD :-}