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). The snd-46xx module is for PCI sound cards that use the 4610 chip, which the Thinkpad has, but it explicitly says it doesn't support these soundcards. The snd-cs4236 module is the ALSA module under ISA cards.
If you are running a Debian or Ubuntu-based system, add "snd-cs4236" to the /etc/modules file (create it if it doesn't exist) so that this module is automatically loaded on boot.
When using the kernel that came with Ubuntu 5.10 (breezy) or 6.06 (dapper), I needed to boot the kernel without PNP? support. This is done by adding "pnpbios=off" to the kernel command line; the proper way to do this is to edit /boot/grub/menu.lst, and add pnpbios=off to the line that starts with
# kopt=root=...
and then running grub-update(8)? to get those options added to all the kernels that are installed. If the pnpbios support is not disabled, then the module will fail to load with a message like "CS4236+ soundcard not found or device busy" and there will be no sound. If you still don't get sound try adding "acpi=off" to the kernel command line as well.
I have the following snippet in /etc/modprobe.d/sound:
options snd-cs4236 isapnp=0 port=0x530 cport=0x538 irq=5 \ fm_port=0x388 sb_port=0x220 dma1=1 dma2=0 isapnp=0
(should all be on one line).
Those are the default settings, but it's possible that your card is using different settings. If you have a windows partition on the laptop, you can 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)
You should also go into the BIOS menu (hold down F1 on power-on), and disable "fast boot". Fast boot means that you are using a PNP? OperatingSystem, so the BIOS won't configure the hardware, assuming that the OS will. You should disable this so that the hardware is correctly initialised. Interestingly, my sound card worked even with "fast boot" on, until I re-installed Ubuntu on the laptop, when my sound stopped working. Changing this setting fixed it again.
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. ''
With Ubuntu Dapper's kernel, my old thinkpad 600 no longer powers down automatically when the machine is shut down. This is because these old laptops use APM, and not ACPI for power management. Create a file in /etc/modprobe.d (such as /etc/modprobe.d/power) and add the following:
options apm power_off=1 realmode_power_off=1
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 HardDisk 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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