Motherboard for T40 series is also used in T41, and T42 series.
Motherboard for T43 series is different.
The T40, T41, and T42 series uses an Intel 855PM Mobile motherboard chipset.
The T43 series uses an Intel 915PM Express Mobile motherboard chipset,
Intel 855PM Mobile motherboard chipset,http://en.wikipedia.org/wiki/List_of_intel_chipsets#Pentium_4-M.2FPentium_M.2FCeleron_M_mobile_chipsets
Intel 915PM Express motherboard chipset,http://en.wikipedia.org/wiki/List_of_intel_chipsets#Pentium_M.2FCeleron_M_mobile_chipsets
There are plenty of T43 motherboards available.
A) Remove ALL power.
Remove the AC adapter (Charger), and Battery. (IN that order)
B) Use an ESD wrist strap, and connect it's alligator clip to a good ground source.
(Electro Static Discharge)
Average cost is around $3 to $6, and available all over.
(I connect to an unpainted surface, of an open, empty desktop computer case )
C) Use a multi-compartment container for the various screws you will remove.
Label each compartment for the area the screw/s come out of.
(You can use a clean egg carton, if no multi-compartment container is available. Label each egg holder )
SOME screws look VERY similar to other screws. DO NOT mix them up.
D) Service Manual: (Free)http://www.tim.id.au/blog/tims-laptop-service-manuals/#toc-ibmlenovo
Scroll down to the line that begins with - ThinkPad T20. (T20 in blue)
Scroll across, and click on - T43
This is a PDF file. The computer you are using now has Adobe Reader on it, which uses PDF files.
After you click on the file name (T43) it may take up to 30 seconds, before the first page comes up.
Have problems using the manual post back in a Comment.
1) If this is your first time you may want to make notes, and drawings.
Use a digital camera, or video camera if available. (Use good lighting)
It's nice to have a Service Manual, but even better to have your own personal record, in case you are interrupted.
2) The motherboard lifts out at an angle. Replaced at an angle also.
3) Make SURE all cables are plugged in tightly, AND rerouted back through the SAME channels, and latches, when reassembling.
The tab indicated in the illustration on Page 87 (PDF file page number)
is above the two keyboard keys shown, but is below the height of the keys.
It is a rectangular tab that you depress with a thin tool. Then the top of the Keyboard pops free.
For additional questions please post in a Comment.