The 8500 128MB does not work correctly in OSX. It will identify the full 128MB. At first it may seem functional until you load something up that makes use of the extra RAM. The application will either crash/freeze or give a colorful distorted mess. The 128MB 8500/8500LE have a different board revision than the 64MB cards so I doubt any of them would work correctly.

If you want 128MB you SHOULD get the same card Jim purchased. You may get only 64MB if you get a 128MB card. Most of the 9250's floating around have only a 64-bit memory interface (many are not even labelled as such) so you will probably get only half of the labelled RAM accessible. Some cards with 128MB and a 128-bit memory interface will only work in OSX with 64MB. If you see only half the RAM locations populated (4 modules instead of 8) you can be pretty sure you'll end up with half of the RAM accessible regardless of the memory interface.

In the end stick with the 64MB 8500 if you want to be sure what you are getting will work.