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. ''
Note: these notes are for a Thinkpad 600. Other models might have completely different codes, case layout, and battery part number!
If you get error numbers on boot such as
00173 00192 00163
Then it appears you have a flat BIOS battery. (Most computers have a small battery to remember settings about the HardDrive? etc when the power is off).
To remove the old battery, first remove the cover for the memory bay by loosening the screw shown in the picture:
To remove the battery, remove the plug and gently slide the battery out of its plastic holder, shown in the picture:
It is a standard Panasonic CR2025 lithium battery, with the leads attached by a neat heat-shrink tubing.
When you plug in the replacement, make sure that the plug is the correct orientation! Black wire closest to the edge of the bay, red wire closest to the memory slots.
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