This is just incase there are any others that came across the theme install issues with 6280 (and probably other phone models) when using an Apple Mac computer.
1. Download the desired theme to computer (hold ctrl and click on "download to PC" Select option "download linked file")
2. Select downloaded file.Hold the Apple key and press "i" which gives you the file info (this can also be done in finder as one of the "file menu" options)
3. Delete the .zip extension so that it just says ".nth" and press enter.
This file can now be uploaded to the phone and installed through Phone director (the program I use) or through Bluetooth file exchange. I presume this is done as easily through the USB data cable also.