Type_X, check in the Media Center forum here because there are themes uploaded there as zip files. In that case, you can download the zip file to your computer, unzip it and install the themes with Desktop Manager. Somewhere here there are instructions for that.
Edit.. here's some instructions. View Document
You have to have the device OS installed on your PC as well as Desktop Manager.
Add again... this one is better: View Document
You have remember where you unzipped the .alx file to so you can find it when you run the App Loader. Best place is to unzip it to My Documents or the desktop.