I'm using Xfce and the screen goes to blank if I'm not doing anything on my mouse or keyboard for a while. How can I set that thins won't happen? Also, is it possible to set the screensaver such that if I'm watching video on the internet, the screensaver won't go on?
You can try Caffeine, it works both with gnome-screensaver and xscreensaver. If you can't install it, there are lots of independent scripts that you can download and use.
If you can't install directly, try with this ppa:
sudo add-apt-repository ppa:caffeine-developers/ppa sudo apt-get update sudo apt-get install caffeine python-glade2
Here is a well known script