1 - Wherever you have downloaded the archive to (probably your downloads folder) unzip the file "Nuke 6.3v4 Mac.zip".
2 - Double click the disk image "Nuke_6.3v4_Mac_64bit_x86release.dmg" to mount it. Then run the installer .pkg which will probably install Nuke to the Applications folder.
3 - Open the Terminal utility and type "sudo chmod -R 777 /Applications/Nuke6.3v4/" exactly as written without the quotes. If prompted, enter the admin password.
3.1 - If step 3 does not work properly, basically what you are trying to do is to change the permissions for your Nuke install folder. So instead, go to your Applications folder, right click (ctrl click) on the Nuke 6.3v4 folder and click "Get Info" (or just click on it and then hit Cmd + i). At the bottom of the pop up box, click the padlock to unlock it. You may have to enter the admin password when prompted. Change all of the Sharing & Permissions settings right next to this to "Read & Write".
4 - Now unzip the file "Nuke 6.3v4 Crack.zip".
5 - Go to the Nuke 6.3v4 folder in your Applications directory. Inside it, right click on the Nuke 6.3v4 application icon and click "show package contents".
6 - Go into the directory "Contents/ MacOS/" within the Nuke 6.3v4 application icon and scroll to the bottom. Delete the "Nuke6.3v4" icon and / or replace it with the identical icon from the Crack folder.
7 - Go into the "plugins" folder within the "Nuke 6.3v4/ Contents/ MacOS/" directory. Move / Copy everything else from the crack folder (that isn't the Nuke6.3v4 icon) into this plugins folder. Agree to "Replace All".
8 - Now, back in the Nuke folder you downloaded, go into the "License" folder and run "Foundry License Installer". If it doesn't patch the License automatically, click "Install".
9 - Enjoy Nuke! That is an order!
10 - Remember to buy the official Nuke software from The Foundry if you begin using it professionally.
(Also compatible with OS-X 10.7 Lion)