Here is a link to the Sony Reader support page (Canada version which has the T-3).
http://esupport.sony.com/CA/p/select...pl?PRODTYPE=74
ADE on your Mac, ADE on your PC and your readers all have to be authorized individually to the same ADE user name and password to swap the DRM'ed books between them all.
ADE 1.7.2 should be compatible with OS X 10.4 according to the Adobe website. I don't think you need anything newer. I use 2.0.1 on my Mac with the latest OS X. However, ADE on the Mac can't "see" Sony readers like it can other brands. You can manually drag-and-drop files from your computer to your readers as long as they are authorized to the same accounts.
The old Sony software (called Reader Library) will work with the 350 and Mac OS X 10.4.11. See links below. It will see your 350 and authorize it. It won't see your T3.
http://esupport.sony.com/US/p/swu-do...&os_group_id=3
Unfortunately the new Sony software (called Reader for Mac) which works with your T3 won't work with your version of OS X. The Sony website says it needs OS X 10.5.8 or later.
http://esupport.sony.com/CA/p/swu-do...&os_group_id=3
Another suggestion is to try to authorize your readers with ADE on your PC too.
Sorry, I don't have a T3 although I wish I did.
Good luck!