If you are using Skype on Ubuntu 7.10 (Gusty Gibbon) on a Dell D630 and have the “famous” internal microphone problems due to the HD-Intel chipset, I’ve found a simple solution, sort of. 
I recently bought a Plantronics .Audio 470 headset at Best Buy for $50. Its a nice headset with good sound quality and a good mic that is also fold-able for good portability.
That headset also comes with a USB adapter which allows you to basically get a USB based sound card so you can use that headset with machines without a sound card (or a problematic sound card/chipset…).
It seems that Ubuntu works well with that adapter. Ubuntu recognizes it as another sound device, as if you have another sound card attached. I attached it, run Skype and configured Skype to use that newly found sound device for incoming and outgoing voice chats and it just worked.
I managed to call people, they heard me well and everything was fine.
The only downside was that it works only in mono, for some reason, so I only heard sound on the left side (when its hooked to another Linux machine that doesn’t have a mic problem or a Windows or Mac machines the headset is working in stereo UPDATE: It seems that there were two devices, one was stereo and one was mono. When I switched to the second one I started hearing in stereo :-) ). It’s still better than nothing and if you have a headset with only one left speaker you won’t even notice it ;-)