there is some MCU has PCA which generate PWN easily. like AT89C51RD ot P87C51FA. but i couldn`t find this chips, i got AT89C52.
but you do not need PWM.

But how to accelerate and decellerate the steps?? i need your help in this case.

DO NOT do this as I say, it is an example, not what your motor need (which I have no idea of).

Set a timer for 2000 counts, step, on timer interrupt, set timer for 1980 count, step, on timer interrupt, set timer for 1960 count, step and so on. For deceleration, after you know how many counts total you are to step, subtract the number of steps to decelerate and at that time do the above in reverse. Of course if the number of step is less than accellerate and decellerate, you have to figure that too.

Erik