Hello,
What version of OS X are you running on your eMac? Did you install the software that should have come with your digital camera?
I remember in an older day that my Powermac G3 would not accept memory cards in the PCMCIA slot under OS X, but they worked great under OS 9. I would verify that the software is properly installed.
I have not tried USB Pen drives on an e-Mac (or on any Mac for that matter). Music should not be a problem... but it could be the media that they are played on. I have had better luck with verbatim CD-ROMS and have had HORRIBLE success with Maxell's. My truck's audio player will not play any homemade Maxell, yet the Verbatim's work just fine.
Good Luck,
Christian