If you have an Ubuntu 8.04 installed on an Eeepc and will be using Audacity, the default ALSA will not work only the Jack Connection would work, but how do you configure your JACK?
Install Qjackctl using synaptic:
1. Go to System->Adminstration->Synaptic Package Manager.
2. Search on Qjackctl and check then install.
3. Go to Applications->Sound & Video->Jack Control.
4. Configure using these settings:
* Driver: oss
* Frames/ Period: 512
* Sample rate: 48000
* Periods/ Buffer: 20
* Word Length: 16
* Port Maximum: 1024
* Timeout: 5000
* Audio: Duplex
5. Click OK then Start jackd.
6. Run Audacity, then Edit-> Preferences.
7. Playback device and Recording device choose Jack Connection.
8. On the lower left side of the tracks, choose 48000 instead of 41000.
9. Record, Play, and Enjoy!
Or, you could upgrade to 8.10 Intrepid Ibex and is fixed by default without going into this trouble. :)