Why does the Back Side of my Mack book Heat up fast...

Why does the Back Side of my Mack book Heat up fast also that slows the other applications to open and respond. I have a MacBook with 2.2 Ghz intel Core 2 Duo processor and 2 GB 667 MHz DDR2 SDRAM. Its almost 2 and a half years i have it and now i m facing problems with it starting from 1) taking time to start when switched on 2)Airport sometimes does not respond well 3) battery life finishing fast and the worst of all 4) applications taking time to open and respond. I have spoken to some people who use Mac and they said its something to do with the the Mac over heating........Plzz advice.