The thinkpads are a series of laptops made by IBM. The older 600 series used Intel Pentium2 processors.
The sound-card on a Thinkpad 600E needs the snd-cs4236 module if using ALSA, despite the card claiming to be a 46xx (and using a module named cs4232 in the older OSS driver series).
(Maybe check out AlsaNotes).
The sound card uses the es4232 driver - this is documented on many pages on the web. However, I couldn't get the module to load - it couldn't find the card. I found this page that helped me... I had to boot into windows to run a utility to configure the soundcard (the ps2.exe file was in c:\windows\options\utility)
rem the cs4232 0x530, irq 5, dma 0 1 ps2 audio address 530 ps2 audio irq 5 ps2 audio sbaddress 220 ps2 audio dma 0 1 ps2 audio enable ps2 audioctrl address 538 ps2 audioctrl enable
After rebooting into linux, my sound worked. (This was a 600E Thinkpad)
Some (or all?) thinkpads (such as my Thinkpad 600) have non-standard microphone sockets. They expect an external microphone to either be powered, or to make contact with a metal ring surrounding the socket, which supplies +5V, and give it to the "tip" of the jack. This is discussed at 
http://www.pc.ibm.com/qtechinfo/LWIK-3QZJKZ.html?up=unknownuser. If you plug in a regular, un-powered microphone then nothing will happen.
Thinkpads in the 600-770 series have a "simple boot" flag which is really a PNP OS=no flag. You should disable it for Linux 2.4, at least if you want the sound to work. Change the BIOS by pressing and holding F1 before you power up the machine, and hold it until the BIOS screen appears. The simple boot flag is under the Quick Boot icon. My sound works ok with this enabled, but see below -- JohnMcPherson
No page links to ThinkpadNotes.
