Running Ubuntu 13 alongside Windows 7

Been thinking about this for a few days now. Even made a live USB stick and looked Ubuntu over. I had a few problems. First, even though I could browse the web on the browser, I could NOT get flash to work for me on it. And when I checked out Rhythmbox (Ubuntu's audio player) to play streams,etc, it had none and no codecs? WTF? And now here's my problem : I am still wanting to install it alongside Windows 7 on my laptop! Is that crazy? And if I did, just how much space do you give Ubuntu and how much Windows 7? Any ideas,etc?