I have Ubuntu-studio 12.04 installed and I really want to have both Xfce and unity desktop, can I install both and use one of them when ever i want login? If so can you give me a little guide. Thanks for answers.
Yes, this works the same as in any Ubuntu installation. The only difference is that new versions of Ubuntu Studio use Xfce by default.
To install any package (including
You'll probably prefer the Software Center, as it uses a simple, graphical interface.
The amount you'll have to download will depend on what components you currently have installed, so it would be hard for me to guess that...but both installation methods will give you this information when you go to install anything.