Problems with 4850!

Please help me, I posted this in driver part but I think that here I might have better help...

I Have the ASUS M2N-E SLI Motherboard, wich has a NVIDIA chipset.
I just made a upgrade to a ATI Radeon 4850 and I noticed that every thing goes "well" until I install the ATI Driver!
After I install de driver the PC starts to crash, not a blue screen, just freezes after some minutes of use!
I am sure that is when I install the ATI driver because I just removed it, the driver only (catalyst still installed) and I am using the PC with "no problems".

I heard that was not possible to use the 4850 as principal grafic and de old Nvidia 8500GT for physx, but I did not know that a conflict would appear just because the onboard LAN is NVIDIA driver!

Please help me, I need opinions!!!

I thought about these 2 possible solutions:

1- Disable the onboard LAN and remove its driver, install ATI driver and see if the problem stops.
2- Install MS Windows XP and see if the problem stops, since I heard that the XP does not have problems with using nvidia and ati drivers at the same time.

What you guys think about it?

Thank you very much allready!!!


Edit:
I disabled the LAN onboard but did not solve the problem!