System Spec
[hardware]:
Intel Celeron 2.6 Ghz
Memory: 512 MB DDR
MotherBoard: ECS L4vxa2 with Via p4x400 Chipset.
Video : Asus Geforce 6600 TD , 128 MB DDR/128 bit
Audio:Creative Sound-blaster 24 bit live
HD:Maxtor 60 GB
Standard keyboard and mouse.

[BIOS settings]
Latest bios updated with ecs flash utility (the bios is flash-able)
FSB bus speed:400 Mhz
FSB clock:100 Mhz
DRAM clock: 166 Mhz
cpu clock:100 Mhz( enabled by auto setting)
cpu speed:2.6 GHz
All memory timings are controled by SPD
agp fastwrite=yes
agp read=no
agp write=no
AGP BUS: agp 8x
Agp aperture size:128
Agp driving control:auto
pci write=yes
pci read=yes
v8link=no
dbi to agp output=no

[Software]:
Win xp home edition with sp2.
directx 9.0c
Video Driver:Nvidia driver 67.66
VideoCard overclocked at : 366 MHz [Core] and  671 Mhz [memory](with RivaTuner at High quality settings for 3d and opengl )
System Driver: Via 4 in 1 driver,5.1.35 version (stable driver)
Using virtual memory aprox 1.5 X 512 MB[physical memory]
Page File Usage: 311 MB
Windows Appearance Interface  is in Performance Mode.

[The problem] :
Regarding the overcloking,  the system cannot manage the agp bus.
if the agp fastwrite , agp read and agp write are enabled in BIOS the system becomes unstable and in games is freezing (including counter-strike 1.6  ver).
if the agp fastwrite , agp read and agp write are disabled the system is stable but  pour 3d performance (9 FPS in doom 3 [with medium settings at 640*480 , all special FX on , ] on  geforce 6600 overcloked  )
If the videocard is not overcloked still the same problem.
Scanned for viruses/spyware/etc  and none found.
Hdd defrag.
With the hyperion driver the problem becomes worse.[the system is freezing without entering any game]
The latest nvidia driver do not solve the problem.Has no effect.
About Conflicts and sharing take a look at this picture:
Image Insert:

160.37 KB

About IRQs see bellow:
Image Insert:

122.46 KB

About memory:
Image Insert:

166.5 KB

Problem Solved. Thanks again for your posts ( none is better then zero   )