Hi Jandreas.
I'm a fan on robotic. Davidgrm was right. Please clarify you question, below are some question basically:
1. What kind of motor to use? (dc, servo, stepper, ect)
2. What is voltage supply for the robot?
3. What is the load carried by the robot while following a line?
4. What kind of sensor to use?
Because, if we didn't decide what we going to use in this project, how a we going to program the m/c (8051), some motor needs driver and some sensor needs backup circuit. So, for me, its better to make some clarification, in order to a archive a good result.
'Learn till you die'
Pian