Try updating everything to Beta 11 (emplode and the player have to match), then try USB again, as USB problems often devlop if you plug in the player before you installed emplode, as it installs the wrong usb driver.

Ethernet should be pretty easy to get going. Make sure you've got a link light on both ends - if you don't, you may need a crossover cable. Once you know the link is good, try manually specifying IPs for both sides of the connection...

Don't even try uploading your music to the player over serial, it's just not worth it.

Matthew