Banding problem (GT200M on ASUS K61IC), driver recs?

[Guest lagopus]

Like many others, I have colour banding problems on my card. I keep getting blocky colours and the transitions between colours (on video or on still images) aren't smooth--it's like working on an 16 bit computer or viewing .gifs. This is especially annoying, as I just got this computer a week ago and desperately need it for photo editing purposes (it's a bit difficult to assess shades in Photoshop if you end up seeing stripes on your monitor no matter how you blur and smudge and blend). I've tried a couple of different drivers (the last few ones from the ASUS site and the NVIDIA site, as well as some from here) to try and fix the problem, but nothing has worked so far. I should have the latest BIOS installed and the latest DirectX and everything set up.

Specs:

Model: ASUS K61IC (-JX099V)

OS: Windows Home Premium 7 64-bit

Processor: Intel Core 2 Duo T5870

RAM: 4GB

HD: 500 GB

Card: NVIDIA GeForce GT200M with 1GB memory

Screen size: 16"

Resolution: 1366 x 768

Here's what TechPowerUp says about the current settings:

Driver version: 186.78

Stream processors: 32

Core clock: 500 MHz

Shader clock: 1250 MHz

Memory clock: 400 MHz (800MHz data rate)

Memory interface: 128-bit

Total available graphics: 2815 MB

Dedicated video memory: 1024 MB

System video memory: 0MB

Shared system memory: 1791 MB

Video BIOS version: 62.94.93.00.09

IRQ: 19

Bus: PCI Express x16

The most annoying thing is that sometimes the images get a bit better if I go to the NVIDIA control panel and let other programs set the colours--but then, I'll end up with a too-bright screen and can't adjust contrast or gamma at all. Can anyone give me any hints about drivers that would be good for this sort of problem? Or is it a known problem with these particular ASUS laptop screens? Or should I just give up and go for a completely different card?