I tried using the Toggle mark occurrences (Alt + Shift + O)
button and also in Preferences -> General -> Editors -> Text Editor -> Annotations
and setting the C/C++ Occurrences and C/C++ Write occurrences. But still when I select a word it won't highlight all occurrences of that specific word.
What I am using is Eclipse Indigo Service Release 2 in XP, with a C++ project.
You can try to activate Toggle Mark Occurrences with icon on Toolbar: