Thanks for the prompt reply Imkantus. I took your advice and deleted the Natit.kext and it hasn't changed anything. So, surely Natit wasn't even required.

1) So, I am wondering if anybody with the same video card (GeForce 6150 SE) has been successful in curing the window wash problem.

2) I can give nforceLan a try, which is on the ipc disc. If it is a .kext file then I should be able to just add it to /System/Library/Extensions. Am I right ?