actually it's not the "/" key but the "\" key that will take you out of fullscreen mode...
I disagree with blacklist in saying that XBMC maybe is not for you. I know plenty of people who use XBMC just for audio playback because it has such a nice interface.
Browsing your desktop isn't so difficult and can be accomplished in 2 different ways. First of all I need to tell you to PLEASE NOT STORE DATA ON YOUR DESKTOP.
First of all it makes your computer slower if you have loads of stuff stored on your desktop.
Secondly, since you are a beginning user for whom a computer is just a tool, when you want to go to the location on your hard disk where the files are ACTUALLY STORED, it's a pain in the @$$ to find it. Please create a folder on another drive or partition (like D:\) or anything you might have. If you don't then just create a new folder on your C: drive to store your music.
This just works better for you in the long run. If you decide to re-install windows someday, you can easily wipe the C drive and install a fresh copy without having to worry that you lose your documents and files. I personally never store anything in "my document" or "my music" or on the c: drive at all, just because i not want to lose any data when i choose to re-install windows...
Now, to get to your problem on browsing your desktop,
Easiest thing to do is to create a new media source. You can find how to do that in the Manual i am writing at the moment. It's a beginners manual and I have started to write it 3-4 days ago so it's far from complete. Browse to the MUSIC section in the library to find all the information you need.
The second thing what you can do is use the "file manager" from XBMC.
In the main menu "assuming you have a standard installation without any changes to the skin" please go to the SYSTEM option on the bottom of the menu and press the "RIGHT" key.
This will open up a submenu with the option "FILE MANAGER" listed.
In the file manager click on "ADD SOURCE" to add your desktop to it.
Next click on "BROWSE" This opens up a browser where you have to browse to your desktop.
Assuming you have windows, browse to:
1 - c:
2 - USERS
3 - (your username)
4 - DESKTOP
then click OK, and OK again.
Now you can see DESKTOP in the list of folders on your screen.
You can click it and browse it. This is what you wanted right?
Adding it as a music source is easier in my opinion. just download the manual i am writing
here
P.S. I am uploading the new version of the manual right now. check your filename, it should at least be version 0.35 or higher. If you have a lower version the upload hasn't completed yet and try again in 5 minutes...