In some opinions it is better then Windows. I will say once you learn how it works you will find that it is was easier to use then Windows and it is more stable when it come to running task for you. Just remember it is a Linux OS which means all software is free and 3rd party. So for example if you want to put music on your ipod you will have to use a 3rd party source app like gtkpod or amarok.
Most games will run under a program called wine unless the game is made by EA games.
You can do a partion on your computer where you give Ubuntu so much room on your HDD so you will have the option to either use Windows or Ubuntu. Make sure to use Ubuntu 10.04, 10.10 is nice but it is more like a beta version for the the next LTS (long time support,10.04 is the last LTS release).
Most people I know that kind find all the software on Ubuntu to fit there needs usually completely drop windows, not saying that you should but many people find Ubuntu easier to use and prefer how it operates.