I had a similar problem with my Lattitude D600 running Ubuntu 8.10. I got a USB Skype phone and selected the HID USB Device in the Skype preferences. It worked great after that. I never got the internal mic to work though. Today I reloaded my system with Ubuntu 8.04 and it automatically detected my internal speakers and mic. I could make a Skype test call without using the USB Skype phone after that.
In both cases, I had to uninstall pulseaudio and switch to esound instead. See the troubleshooting steps in this link for more info:
Just ordered a Dell Mini 9 and I wanted to make sure Skype works with it before I placed my order. It works, with a few tweaks. Ubuntu 8.04 seems to be more stable and has better hardware detection that Ubuntu 8.10. I'll probably stick with 8.04 instead of upgrading to 8.10. My Mini 9 just shipped today. Whoppee! It should be coming in the mail soon.
I'm happy to see vendors promoting Linux. After suffereing with Vista on my D600 for almost a year, I decided to switch to something else. Ubuntu seems to be the most popular, so I wanted to get on the bandwagon. Dell is one of the few vendors who sell preinstalled Linux. I heard that Dell telephone support is lacking when it comes to Linux. That's why I decided to participate in this forum and add my 2 cents. This is my first post. I hope it's helpful to the Dell Ubuntu Linux user community. By the way, Dell should add Ubuntu and Linux to the tags for posts like this.