Well, the latter I can avoid by not letting wasted people in my room, and also keeping the tower under my desk. That way, hopefully, there would be less risk of it falling. The former I cant really do anything about, besides chaining the thing to my desk. Which will make it an even bigger target.
I wouldn't worry about it. Just keep your doors locked, get to know your roommate well (if you have one and you don't already know him/her), and hope you don't get burgled.
Laptops are a hot item, desktops are a bit harder to steal.
If you're that worried, get one of those cable-locking devices and tether it to your desk