anyways, here are the steps I used to get my HD4890 working on 10.6.2 with native resolution.before installing these packages, it was showing only ATI device with 256MB RAM in system profiler!
I am totally new to Mac and I can understand the problem newbies ( like me ) facing while installing patches, kexts, etc or understanding about unclear steps given on some topics,so i have given detailed steps below.
1st of all, here is the proof that it is working ( atleast for me )
1. Download attached "Packages.zip" file. and extract it. you will find 3 package files inside named "Enabler_for_Nvidia_and_multiple_ATI_cards.pkg' , "QE_CI_Exotic patch 10.6.2.pkg" and "QE_CI_Exotic_cards.pkg"
2. 1st run "QE_CI_Exotic_cards.pkg"
3. Now run "Enabler_for_Nvidia_and_multiple_ATI_cards.pkg"
4. Now run "QE_CI_Exotic patch 10.6.2.pkg"
Let me know if this worked for your or not.