I am dual booting Windows 8 with Ubuntu 12.10. When I use Windows 8, it hardly ever heats up, while in ubuntu it heats up very quickly. I am using a netbook and I do not want to give up at Ubuntu, but also I do not want to upgrade any hardware. the netbook is a acer aspire one d257, it has a intel atom n570, igb ram and 6 cell lion battery. i do not know what graphics card it has.
If you are having problems with battery, CPU or overall overheating of the machine I suggest you try TLP. Originally designed to increase the battery performance, it also offers a lot more than just that !
Also, if you type "sudo tlp-stat" (after installing) you will get all the information you need out about your machine, and I bet that is going to help a lot of people here to help you even better.
Still, it is imperative that you find out your graphic card type. If it is an NVidia, there are ways to control the fans through its driver's software (Not sure if that is also possible if you have an ATI or INTEL).