From what I can tell, the SanDisk Sansa player is supposed to be supported on Mac OS X. SanDisk has a special forum dedicated to the Sansa, and has a subforum for Mac and Linux. You might want to post your question there if you have difficulty getting your Mac to recognize the player.
This is what I have found out, as I understand it. First version released was compatible with Mac/OS X and worked well. After a couple of firmware revisions people started having problems connecting, synching etc. Some reverted to older firmware versions and continued to use them without problem. Now, there have been several firmware revisions and they do not work at all. The older firmware is no longer available (that I can find) and even if it were, one would need to connect to the computer to install it.
The player is a nice product but do not understand why a company would ignore/write off a significant - and growing - share of the market. Have sent a message to SanDisk inquiring about all this. If I receive any useful info will post it.
For those of you trying to find out how to make your e250 or other sansa mp3 players work on your mac os x (10.3.9) just follow these easy instructions.
before connecting to your computer, switch the USB mode to MTP
Now connect to your computer ( it will do Nothing)
Now disconnect the mp3 player(just unplug it)
Now change it to MSC mode
Now connect it and bualla, it works!!!
i dont know why but it does. and if doesnt work for you then you suck
you can always just downgrade but you need a windows computer to downgrade.
I purchased a Sansa Sandisk player (2gb e250) via woot.com, mid-November. This device mounts as a removable storage device in OS X. As such, I simply drag and drop songs from iTunes to the desktop, and then into the "Music" folder on the device. Works great. :D