Guys whats the best utility to check RAM ?

http://www.memtest86.com/

I don't know if it's the best, but it's the one I use. It seems to work well enough.

the best ram tester are those machines that cost $150,000!......so I guess the next step down is memtest86

Memtest86 is good and it's what I use, but Memtest86+ is supposed to be better.

I remember that i got a beta memorey tester from microsoft long time ago, any news about it ?

Yeah, they were working on one XP_2600, but I never heard of it being released and I would hardly classify as being "the best".