Thanks. It turns out that the key was going into "Settings" and changing the USB mode. I also found out that sequence is important. One must turn off the player, connect the cable, then turn on the player. In this mode it shows "Disconnected" for a few seconds, which changes to "connected." The directory turns up as "Sansa_e250." I'll keep an eye on Rockbox for news of his success at a Linux port. From what I hear, only a couple of players and a CD from Sansa were provided. He has to reverse engineer the boot loader.
mount Sandisk e250 under linux
"The player has two modes. One mode is like an external USB drive and supports MP3's. That should work just fine for Linux. Two drives will show. One is the internal memory and the other is the SD card."
-- The easiest way to figure the cost of living is to take your income and add ten percent.