Hey again,
In that case it might just be simpler to do:
sed -e 1,2d -e 6d FILENAME
The reason the command above removes any line starting with a pound is that I write answers in too many different languages ;) The proper syntax for this command (although, actually, it was syntactically correct (no errors) but didn't do what was expected) would be to do:
sed '/^#\(ifndef\|define\|endif\)/d' FILENAME
Best wishes,
Mike