seems seized?

1986 Toyota 4 runner  22re engine, Hears the deal loaned the truck out,(first mistake) , they said they herd some knocking,like it was coming from the outside and below their feet, lights seemed to have dimmed on them , was losing power in the motor. they said they thought that it had something to do with the battery, and called me for a jump. got there bought a new battery put in it, then this is what I find,... the starter seems to be trying to engage, but has a sudden stop to it, took the starter off, check the fly wheel teeth good, (good shape) took the starter down to have it checked, (good shape) its a Manuel truck and has had problems with the clutch in the past, and am always having to add fluid to the master cylinder, now where the clutch has been a problem in the past I was hoping that it could be that some how the pressure plate,throw out bearing and shift fork could be the issue, I don't know how to tell if the engine is seized, and was wondering if any one has ever had a problem like this and what steps you took to figure out what was hanging it up? I need some insight for my next move.  
                           Please Help.Thank you