and how to change to the GUID system from mbr system?which tools should i use?

only one HD? you can´t, you need a clean install and select the correct partition scheme.

GUID

Which are the benefits to have GUID vs MBR partition? GUID is more close to a real mac?
At the moment i can see a bad thing... i can't backup the partition with AcronisTrueImage. It can't see GUID partition... so i'm looking for something else...

Use clone backup utilities that are designed to make an image of a Mac, not PC. Google is your friend. =D

superduper and CarbonCopy crash about 4 seconds from start create image... i'll try with diskUtility. If system is damaged (don't start anymore) is it possible with disk utility to restore image and boot again?

here's a very strange thing.. i added another 512 ram to my system :) and guess whats my xbench score now? 31.06 :))
http://filebeam.com/d5d7b77d210b5f27...b4cdaab663.jpg

Your memory test score has dropped considerably, do you have many options in bios for memory?

i have and OEM PC meaning restricted bios settings :(.. why did i bought an HP ..why :)

Insanity?

Try re-arrainging the memory sticks, it sometimes works wonders!