I just installed Ubuntu-gnome 32 bit 13.04 on my intel iMac, but when I try to watch youtube videos in fullscreen, its very choppy and laggy, is it possible to fix it somehow? I'm using adobe flash player 11.7 with chrome pre-installed
Without more information about your video card and Xorg setup, the only thing that comes to mind is bad video drivers.
If you don't mind using the proprietary drivers, look here:
If you prefer the free drivers try this:
After having read (one of) those, feel free to update your question and post your progress. I'd be willing to lend you a hand (but not hold your hand).