Yee, i know...but i'm a bit green in all this, so it's took me some time to figur out what's wrong
I'm back to business

I was too impatient to wait for my hard drive RMA... I just went to shop and bought another HDD. Now i'll have 2 HDD (when my faulty will be exchanged).
Back to file corruption... I checked new drive (WD aswell) and there was no errors on this one

. So my bigest question was, is file corruption problem is solved? I downloaded MOBO driver for DFI NF4 from nVidia's site, nForce4 AMD Edition v6.70 (the same file i was testing before). Again i saved file on desctop... u won't believe. file was corrupted again

, so it wasn't hard drive's fault.
As before, in this post, was mentioned memory, i ran memtest from
http://hcidesign.com/memtest/ and there was an error at 22% (after about 2min). As i was runing my memory at factory setings 200MHz, but rated frequency is 275MHz (550 effective), i went to BIOS and changed memory frequency to 275MHz. After i ran MemTest again, this time 20min 200% no errors. I downloaded DFI driver again, this time everything was fine, no sign of corruption

.
I wasn't sure is there anything to do with memory, but looks like if you runing memory with lower frequency as rated it's can cause file corruption.
I still need to do longer tests to see if everything is O.K. for 100%. But so far it's step forward, anyway.