You need to find a friend with a PC who will let you do it or set up a windows instance using Parallels or VMWare or BootCamp. You should also be able to do it ont he Mac with the CD that came with the device.
The OS and instructions are in the yellow sticky at the top of the 9500 section.
Have you tried just plugging it back in to the Mac Desktop Manager and running Application Loader? 507 just means the software needs to be reloaded. I've not used DM for Mac that much so I can't say for sure, but it may reinstall the software.
The MAC DM is a bit iffy when it comes to installing an OS, not from your carrier. Mac DM version 1 would not allow it all, version 2 will in some instances, however, it is still best to find a Windows PC or use a Windows instance on your Mac.