I would hardly call that a crash. 😛 I had a similar problem with my iBook when I was still trying to treat it like my fairly powerful desktop and before I bought more RAM. Every now and then when I would have iTunes, Acqlite, VLC, 5 browsers, etc. open, that would happen. I had two options... Leave it alone until it caught up to itself, or, more frequently, use the force quit option. If you experience something like this, never try to go to the pull down menu to get to the force quit menu, as it will likely not even have the system resources to do so. Use the keyboard shortcut that was posted earlier.
On another note, I have no idea why that is happening if you are only running what you posted... any help from a more seasoned mac user?