so this advice helped me too eventhough i have an inspirion 6000. I found out why. It matters WHAT ORDER you install your drivers. check out http://support.dell.com/support/topics/global.aspx/support/dsn/en/document?&docid=1A0C0937D62A8739E0401E0A55174744
Article ID: 303237
I uninstalled the modem driver and then the audio driver. I then re-installed the audio and wah-laaaah- i had sound. Then I installed the modem driver AFTERwards and everything works fine.