How to get Sound with PS3 connected to 2408WFP using HDMI cable?

Hi, I have the Logitech X-540 5.1 speaker system, a PS3, and Dell 2408WFP monitor.  I used the HDMI from PS3 to Monitor no probs and the image is great. I have no sound though. I've tried so many different configurations and nothing seems to work.  I'm wondering if i've missed something and someone could help me out.

In short, I have:

1) HDMI from PS3 to Monitor

2) all wires from X-540 Speakers to sound card (green, pink, black)

3) Monitor is connected to computer using DVI

How can I get sound without having to continously switch around cables?  What setup would I need?

Also, which settings would I use in the "sound settings" in the PS3 menu? do I use HDMI or the red/white audio component one?

Thanks for your help!