Natit v0.02 works for dual displays on many Nvidia systems and it is what I am using. I am also re-posting Natit v0.01, which should work for VGA/DVI Nvidia cards, for people who have problems with v0.02 and want to try something else.
However, v0.01 and v0.02 are very similiar, v0.02 merely adds the "@0,NVMT" key and value. For more information on these key-values pairs and how these dual display versions of Natit for Nvidia was developed, see these threads:
Now for people who have problems, here are two general suggestions:
A. Make sure you are using a clean install of 10.4.8. People who upgrade to 10.4.8 (or mess with the Nvidia kexts) often have problems.
B. Make sure you follow these instructions (specifically removing the .kextcache and .mkext) when installing Natit (again, these instructions and the original idea of Natit are credited to Omni).
(1) Put the Natit kext in your /System/Library/Extensions/ folder. (2) Correct the file premissions: sudo chown -R root:wheel Natit.kext; sudo chmod -R 755 Natit.kext (3) Remove the cached and packed extensions: sudo rm -f /System/Library/Extensions.mkext /System/Library/Extensions.kextcache (4) Reboot.
UPDATE: Natit for dual display works with Leopard (10.5) too.