I have tried to install a bunch of different plug in's however I was only sucessful with http://www.adobe.com/support/downloads/detail.jsp?ftpID=4582 ... Unfortunately, it is not compatible with Nikon 5100. Is there another plug in update that I need to install to be able to view and edit my raw images from a Nikon 5100 in PSE 7?
No, there isn't. You either have to upgrade to the new Photoshop Elements, or else download the latest DNG converter and create digital negative copies of your images. Those can be opened with the Camera Raw that you already have. There will be no more updates for Photoshop Elements 7, and that includes the Camera Raw plug-in that is compatible with it.
Of course, another alternative would be to add Lightroom to your arsenal. It would give you a lot more options for working with your raw images. But that is a decision that you will have to make.