Advice in small(mb) benchmark please.

AtiTools

You can DL it from here in the DL section.

www.guru3d.com

It has a small bench feature that shows, 'roughly' how your rig compares to others w/ different gpu's. Its not the most widely used, but it will help you gauge performance if you are looking to OC a little.

Is it the square that indicates fps?
I was looking to something more complex....

Videocard Stability Test...
http://freestone-group.com/video-car...ility-test.htm

You can always run over to PCPitStop and get a fair comparison.

When i start it it says an ati card wasn't detected and most of the functions have been desactivated.And i can't overclock.
But i've seen other people with nvidia cards overclocking with ATI Tool.
Why does this happens?

becuse you are using the wrong version or the wrong program. The program I mentioned is AtiTool...not AtiTrayTool. TrayTools will only work on an Ati card I believe and has benchmark function that actually gives you a test score. AtiTool is a generic that will work for both Nvidia and Ati cards, it does not have the benchmark function but does have an atrifact tester and fps report.