Hi,

I have never used Linux, they are lot of Linux,
1) witch one should I install ??
2) I have windows xp , should I format my pc and then install Linux, or the installation do that ?

Thanks, your help is appreciated.

You should probably keep xp until you're comfortable with Linux. The partition tools which come with some distributions allows you to 'resize' partitions so you can shrink the xp partition and create a new partition for Linux (I recommend a minimum 40GB for Linux and data).

You can download several distributions as a "Live CD" and see which one you like best. Some live CDs worth trying include:

Fedora
K/Ubuntu
Mandriva
Open Suse
Mepis
Puppy

The Live CDs run much slower than an installation to disk, but they give you a chance to try things without installing.

I find Ubuntu good for normal desktop use, but I like CentOS for server use. CentOS has a live CD as well. If you're unfamiliar with what a live CD is, it is a an image of the OS that boots up entirely off the CD and requires no hard disk installation. They can be very helpful in troubleshooting problems with a system that can't boot off its hard drive.