How to know if an UNO is from the very first releases ?

Hi ! i have a friend that has an UNO wich doesnt seems to be stable. I have readen that using IDE 0022 and flashing the DFU could help:
http://firmata.org/wiki/Main_Page

If your Uno is an early model, you may need to use the dfu-programmer tool to flash the 8u2 firmware

My question, before flasing, is :
-sure there will be no damage with flashing ?
-how to recognize an earlier model of the UNO ?

Depends what the issue is.

There is a bug in the firmware of the 8u2, that mostly shows up when using Linux. This is the issue that reprogramming using DFU should fix. Details of how to check the version your 8u2 is at are here.

http://arduino.cc/forum/index.php/topic,53638.msg384647.html#msg384647

All boards that have shipped so far are running the original firmaware on this chip.

The other issue with early unos was problems with the version of optiboot (the code that handles uplaoding sketches to the chip) that was on the board. Details and fix here

http://arduino.cc/forum/index.php/topic,28074.0.html

HTH