i have a 97 bmw 528i
(SAME BODY AS 2000 M5)
and someone is selling me a complete 2000 bmw m5 motor with all the wires and ecu. My question is, will the motor fit into my car with no problem and what else will i have to change or get to make it fit and have it running

the transmission for an m5 is completely different.
also the s62 (e39 m5 motor) has different mounting points and the entire layout under the hood is different.

good choice of car though. i have the exact same one. :)