I don't know if EDO will work or not. The memory on board and in the expansion module are both FPM. Also, I have had 486 boards that will not take EDO memory so they are not always compatible.
After further investigation there are two rather annoying problems with the added 32m of memory. First is the fact that you can only run in 16 colors, anything higher causes errors at start up and the display properties not set up correctly error. Second is that even with hibernation enabled and the hiber.dat and hiber.bin file correctly created it will not hibernate, causing multiple errors instead and eventually requiring a power cycle. Also the bios at boot always reports that hibernation is not available.
I believe that both of these problems are BIOS related but I don't forsee any way around them since there is no update available for the BIOS and I don't even know if it is reprogrammable.
Given the above if anyone wants to buy a 32m sodimm the information is below. I have only dealt with this company this one time. They were a little slow (around 1 week via usps from NY to VA) but the product is as described.
The item you want is:
LGEN0323F1 GENERIC -72 PIN 3V FPM SO DIMM 32 meg $39.49
If the link doesn't work just pick the laptop SODIMM link from the first page.
They also list a 32M module for the Dell Latitude XPi CD M166ST with part number LGENO323F2 and the same price. I don't know i f there is any difference, they only one I tried is the first one I listed.