Hello there!
I'm working to restore my ancient Dell Latitude XPi P133ST laptop, after I stupidly killed it by dropping the DC-DC converter in the wrong spot while 12V were on the board. Yikes!
I bought a P100SD off eBay and, after thoroughly testing it, I declared the mainboard dead and the backlight inverter literally burnt. I reused the DC-DC converter and, lo and behold, the P133 board is still alive! But I've encountered a few issues:

1. Only half the keyboard works: I tried with two keyboards I have and both of them had the same non-working keys, so I'm guessing the two connectors on the board might have some issues reading the matrix. It's not a PS/2 issue, because a keyboard connected to the rear PS/2 port will work perfectly fine.
2. The trackball is not detected: again, tried with the two I have, none of them works. Windows can't detect anything on the PS/2 bus. I checked continuity from the mainboard to the trackball and all traces are good, and I also get 5V on the trackball assembly. My guess, now, is that the internal PS/2 mouse controller is dead.
3. I can't use my display. The P133ST originally had a 11" SVGA TFT display, but the screen is completely cracked. The P100SD came with a 10.4" SVGA DSTN display (I know it will look horrible, but at least I'll get a screen!). I guess I'll need to modify the BIOS ROM to flip some bits around to change the display type, but I'm also afraid that part of the driver circuitry on the mainboard might be slightly different.
4. Last, they use a 7.2V NiCd CMOS backup battery that, of course, has leaked but without too much damage. I don't know where to find a replacement.

Most of the stuff I need to check would easily be referenced with proper schematics, but it's quite difficult to get such technical docs for a laptop that predates most websites currently online. If anyone happens to have any experience on this family of machines, I'll greatly appreciate your input!