Here are the specs for your computer: http://www.emachines.com/products/products.html?prod=ET1352G-03w
There are claims of "expansion" capabilities on this computer. This could mean RAM, 2nd. HDD, PCI cards, etc.
Given the many different models and variations. I would suggest that you open the side panel and look at the inside. Locate the present HDD, and look for space right next to it to add a 2nd. HDD. Most inexpensive computers do have space for a 2nd. HDD. The service manual will explain better.
If you decide to add the 2nd. HDD, turn OFF and disconnect power to the computer, and wear an anti-static wrist strap before you begin any work, and follow directions in the manual.