does anyone know if i can take the 4x4 front end from a 90 model geo tracker and will if fit without any modifications to the x90. one is a standard 5 speed and the other is an automatic

the auto should have 4.62 gears and the Manuel should have 5.12's in it, other than that I think it would work.

I have done the 2X to 4x swap. on a X90. You will need the 4X cross member also you will need to cut out the "left" upper diff. mount & weld it into the frame as your 2X is missing the mount. For some reason the "right" front diff. mount is there.

the auto should have 4.62 gears and the Manuel should have 5.12's in it, other than that I think it would work.

so i could just change the rear end to make sure the gear ratio is the same?

I have done the 2X to 4x swap. on a X90. You will need the 4X cross member also you will need to cut out the "left" upper diff. mount & weld it into the frame as your 2X is missing the mount. For some reason the "right" front diff. mount is there.

is this a very difficult conversion? can a novice do it? would you keep the standard transmission, and will the transfercase adapt to it.

The transfer case will not work on the 2wd trans as far as I know, the 4x4 trans had a spline count change around 1995 or so , it went from a fine spline say in 94 to a coarse spline in 96, so you have to match the trans to the x-fer case and change the output yokes to match the trans fer case, the u -joints are all the same as far as I know so it would be easy.

The gear ratio in the x90 should be 4.62.  All x90s got the 4.62s, no matter if they had a manual or auto tranny.  So if the tracker has an auto, the front end will have 4.62s as well, so no rear gear change needed.  If the tracker has a 5 speed, then it has 5.12s, so you would have to swap the rear third into the x90 to match the front.
There is a possibility the x90 has a dummy tcase on it (dummy tcases are most commonly found on 2wd x90s and 2wd 4 door trackicks....some, but not all, had dummy tcases).  Look under it, if it looks like a tcase, but the front output is capped off (no hole), then you can just unbolt the dummy tcase and bolt on a real tcase (the tracker tcase will work).  If this is the case, then you already have the correct rear driveshaft as well (length and spline count on the slip yoke).  If it doesn't have a dummy tcase, then you will have to find/use a 4wd tranny.....and the rear driveshaft will not be the correct length, nor will the slip yoke have the correct spline count on it (2wd trannys have a different spline count on the output shaft, compared to the tcase output shaft).  So you will have to find a driveshaft that is the correct length (not sure if the one off the tracker will be the right length or not....I would say yes, but don't know for sure).
Some other info....
all sidekick/tracker/x90 tcases from 89-98 will bolt onto any tranny from the same era.
all sidekick/tracker/x90 trannys from 89-98 are interchangable.
if you swap in a 4wd tranny and tcase (and did not have the dummy tcase), you will need to swap crossmembers as well (they just bolt on, so no big deal).
the output shaft of the tcase changed in 96 from a 26 spline output to a 16 spline output.  So you will have to use a slip yoke or complete driveshaft that will fit the output shaft.  All driveshafts from 89-98 used the same ujoints, so you can swap slip yokes from one driveshaft to another, if needed.