I have managed to upload some tunes! I still can't get VPC to work (either with USB or ethernet), but who cares?! Last night I created a new TCP/IP setting just for the empeg, and suddenly JEmplode saw the empeg and everything started working.

Here's what I did, step-by-step (for those who are interested):

1. Borrowed a PC. (First one didn't have a CD drive, 2nd one's CD drive was broken! So I went on line and....)
2. Downloaded latest Emplode software and empeg car software (slowly...)
3. Drank a lot of coffee and tapped my fingers on the desk.
4. Hooked up empeg with serial cable (very old PC so no USB)
5. Launched Emplode software. Doesn't launch - need Winsock 2.
6. Download Winsock 2 from web. (Slowly...)
7. Launch Emplode. Needs newer version of Internet Explorer to work.
8. Download IE5.5 (reeeeally slowly).
9. Ok. Launch Emplode. Woo-hoo - it works!
10. Upload latest empeg car software to empeg.
11. Empeg car shows up in emplode and starts downloading from player.
12. Assign the following info to the empeg:

IP addres: 10.1.1.1
Subnet: 255.255.255.0

13. Cheer up, go home.
14. Plug empeg into Mac via ethernet crossover cable.
15. Create new TCP/IP setting on Mac with the following info:

Connect via: Ethernet built-in
Configure: Manually
IP Address: 10.1.1.2
Subnet mask: 255.255.255.0

16. Launch JEmplode.
17. Set JEmplode options to 'Ethernet Broadcast' and click OK.
18. JEmplode brings 'empeg car 10.1.1.1' into view and starts communicating with the empeg.

So that's what worked for me.
Thanks to all of you for your ideas and help!

Sally