get rivatuner then do this:
http://www.guru3d.com/rivatuner/
Unlocking The 6800NU
Step 1. Install Riva Tuner
Step 2. In the MAIN tab, click on CUSTOMIZE in the TARGET ADAPTER area
Step 3. In the popup menu, click on the CARD icon (LOW-LEVEL SYSTEM SETTINGS)
Step 4. Click on the NVSTRAP DRIVER tab.
Step 5. Check the box next to ALLOW ENABLING HARDWARE MASKED UNITS. Select CUSTOM in the ACTIVE PIXEL/VERTEX UNITS CONFIGURATION dropdown. Click the CUSTOMIZE button.
Step 6. Click in the BIT FIELD/BIT MASK column to insert a checkmark to the left of the row for PIXEL UNITS marked disabled. Do the same for VERTEX UNITS.
Step 7. APPLY and OK buttons as required, then restart.
Step 8. Go back the NVSTRAP DRIVER tab. You should now see Custom (16x1,6vp) Indicating that all 16 pipelines (instead of 12) and all 6 vertex units (instead of 5) are enabled.