I have a 98 Tacoma 4x4 w/2.7L 4cyl engine, that won't start. When I try to start it, all I get are clicks. I checked the battery and connections. All are ok. Could it be the starting solenoid? If so how hard is it to replace? Thanks

you say you've checked the battery? was the battery load tested? was the battery placed on a battery charger to see how many amps it took, and for how long?
have you tried a known good battery? this is usually the 1st things to check, if the battery has a week cell or 2, maybe more, other electrical things ( lights, radio, etc ) will work fine, but the battery will lack the amps to make the solinoid work correctly.
once the battery checks out ok, then move to the starter motor assy.
hth
Rick, Ore