Installation instructions for the ThinkPad 340
The ThinkPad 34x is equipped with IBM's 486SLC2 meaning its double clocked, running at a total of 50MHz. Since this machine has a maximum of 12MB SDRAM and NO Math Coprocessor (FPU), getting Linux to work on this will machine is extremely difficult since most distributions need an FPU or FPU emulation. Using swap is recommended. For convenience you may hook up the target HD to a desktop computer because the 34x lacks CD and USB support.
Unless you are confident of what purpose you will give to your ThinkPad, I recommend to use a different one with an FPU and more RAM!
Distro specific Instructions
Slackware 3.1 has reported to run successfully, but I managed to boot Slackware 7.1, being the latest Slackware that did not require an FPU. To load the kernel one must append floppy=thinkpad since all thinkpads worked with an inverted style connector, and as consequence will not boot properly. During the installation it is recommended to set the TERM= variable to the suggested monochrome terminal, as during the installation is mentioned.
NetBSD isn't Linux but is also a candidate for use on extremely old ThinkPads. I did not however manage to boot 6.1.5. It hangs and reboots at bootdisk 5 (again perhaps due to the lack on an FPU).
Debian <=2.0 is no longer maintained but it will theoretically work. 1.5 is recommended since that does not take extremely long to boot.