How to install Dual Operating System?

Hi,
Can you please help me. I have a single Hard Disk with 2 partitions. My computer has a 2GB RAM and 2.4 clockhertz.
I already installed Windows XP.
But some of the applications are not working properly.
I ask my friend about this and he told me to install different OS. Now I want to install Ubuntu 11.04.
Is there any compatibility issues I might encounter?
Do I have to back up fist my files before installing this OS?
Please help me.
Thanks you in advance.
I would appreciate if you can show me steps on how to do this.
