AutoHotKey can do it.
After you download AutoHotKey, go to Notepad and type the following code:
Media_Play_Pause::Send, {Space}
Save the file as "Keyboard Play Key.ahk" and run that file. (You can save the file anywhere you want and replace "Keyboard Play Key" with anything you want.)
Now, when you press the "Play" key on your keyboard, VLC will play/pause.
Note: The VLC window has to be selected for this to work. I will try to find a way around that.