Ubuntu these days comes on a live CD so you can test it out on your PC without having to install it first. This is a good way of checking hardware compatibility and to see if you like its features. If you are happy to use Ubuntu over Windows, the CD contains an installer to allow you to permanently install it to your hard drive.
The greatest determiner for switching to another OS is: 'Can it do the tasks you want it to do as well or better than the previous OS?'. What sort of things do you do on your PC? It may make a full switch turn out to be a negative experience if you find out something you do often is only able to be done with a program that's only available for Windows.
The Ubuntu installer allows for Windows and Ubuntu to share the same hard disk in what is called a 'Dual Boot' configuration. Many people set up their PC like this as they still need to access applications on Windows that are not avaiable on Ubuntu (ie. Games). This can be a good compromise if Windows apps are rarely used. Otherwise, another option is to use virtulization software such as VMWare to allow Windows to be 'hosted' within Ubuntu so the apps you need can be accessable. WINE (WINE Is Not an Emulator) is another way to run Windows apps under Ubuntu, though it can be hit or miss depending on the app.
If you haven't already, I suggest downloading the the latest Ubuntu CD from
www.ubuntu.com and trying it.
