Inspiron 1520 overheating and shutting down unexpectedly

I have an Inspiron 1520 that recently has started to shut down without warning. The shutdown has occured on 4 occasions, the first 3 while playing a game (Football Manager 2009 if this helps) but the fourth shutdown occured while browsing a website with no other programs running. Its worth mentioning that the laptop can get quite hot and through searching various sites i believe it could be shutting down due to overheating. Any advice on fixing this myself would be most appreciated. The laptop was purchased in August 2007 so i'd hope that it wasnt on its last legs. Thanks in advance.