Well I've completely beat COD4 on veteran (twice!) and will (one day) be bothered to beat 5 (I'm about half-way through), but the one bit of advice I can give is be patient - and learn where to go. Chances are if you try something, it works, and you die later on - that move will work every one in three tries, so keep figuring the puzzle and you'll crack it.
Miracles advise above is sound - learn where the enemies spawn and try and stop them ASAP. There are some "difficult" areas that can be easily beaten with the technique he explained.
Miracles advise above is sound - learn where the enemies spawn and try and stop them ASAP. There are some "difficult" areas that can be easily beaten with the technique he explained.