i was just wondering how hard and how long should i take to replace my tranny on my 96 z34 in my drive way

 

Trying to replace any FWD trans is not exactly something you would want to do without a lift and an engine support. Replacing the trans involves removing the engine cradle and supporting the engine while the cradle is out, you will need to realign the cradle after reinstallation and a wheel alignment is highly recommended.
The 3.4 in the Monte isn't exactly mechanic friendly even with the right equipment. If you do attack it you will need to make sure the car is high enough to get the trans out from underthe car, the jackstands will need to be under the body. The other option of doing it in the driveway would involve pulling the motor and trans together from the top. Again not a easy thing to do. Time wise either wayI would be willing to bet you would be looking at how many days instead of hours.

My suggestion, as someone who has worked in GM dealerships and done this many times, would be to bite the bullet and have it done instead of trying it yourself.