Q: why is my mac running so slow?

It's running slow because you don't have enough ram installed for Mountian Lion.

If this http://www.everymac.com/systems/apple/imac/specs/imac-core-2-duo-2.66-20-inch-al uminum-early-2009-specs.html is your imac, you can nstall a maximum of 8gb of ram. I would recommed you do that, the real life minimum for mountian lion is 4gb. You should buy ram from an Apple friendly vendor such as http://www.crucial.com/ or http://eshop.macsales.com/

You don't have enough ram. Take a look at how to use Activity Monitor http://support.apple.com/kb/ht1342 and you'll get a better understanding about ram use. Open Activity Monitor, it's in your Utilities folder, and run it while you use your computer for a few hours. If your pageouts are more than your pageins, you need more ram.

Installing ram is easy. The MacSales link I posted above has videos that show how to install ram in your model.

You're confusing storage with memory. When you speak of movng things your talking about files, programs and things are stored on your macs hard drive. Thats not your issue. Your problem s ram, random access memory, an electronic tye of storage. RAM is not physical storage, you can't move nytning to make more ram available, you can only add more.

Have a look at Macsales (OWC) or Crucial for the exact RAM for your Mac. Both companies come highly recommended on here. Both sites have easy to follow RAM selectors to guarantee you get the right chips:

http://eshop.macsales.com/shop/apple/memory/iMac

http://www.crucial.com/

My advice would be to upgrade to as much RAM as your computer can use and you are happy to pay. RAM needs to be added in matched pairs. Find your Mac on either of the sites above and see what your options are.

Click on the various links in this thread that the OP have provided for you for your answer.