If your Mac is overheating perhaps you have a dead fan or sensor. Run a Hardware Test
Step by Step to fix your Mac
The 13" isn't a 3D gamers machine, it will overheat the pitiful CPU graphics it has.
Mac video card performance
Yes, the cooling pad does assist in keeping the machine cooler according to others who have posted here have said, however it's not as good as there isn't any vents to increase air flow.
Keep the machine in a cool sub 75ºF enviroment if gaming.
Know that the higher the fans go, the more dust it inhales and collects at the back grill behind the fans.
If your out of warranty/AppleCare (or if in it) see about getting those cleaned to increase air flow.
http://eshop.macsales.com/installvideos/
Ideally a Windows 7 3D gaming tower is a better machine, as you can clean it, upgrade the video card and there are more games.
http://www.cbscores.com/index.php?sort=ogl&order=desc
However a Ps3 makes a decent cheaper alternative and it doubles as a Netflix, YouTube etc on the HDTV.