My guess would be t have the shift lock solenoid checked out (I think thats the name...the relay thing that tells it the brakes are on to shift to gear). I am pretty sure that will cure your locked shifter problem (not 100% though).

As for the tranny vibrating and the blinking "S".....the S on your dash means you are in "Sport " mode..in otherwords overdrive is disengaged. These indicator lights do this a lot but it may also mean your tranny is being put in and out of overdrive mode a lot. Not exactly horrible but get it looked at.

The vibrations could be several things...

Check the alignment....it can cause some weird feeling in the car
Also check the axles while your there (preventative)

Possible torqque convertor issue (they get old and wear out...20 year+ old cars are old and worn).