help me

help me on line follower robot

hi ppl...am new to robotics....i hav 2 do a line tracking robot which can trace lines effectively and doesnt repeat the travelled path....
am doing this for a competition n also 2 get an idea on robotics

it must be a 12v,autonomous robot...
the robot must be able to reach various points in the arena within the specified time limit.
those points will be indicated by a grey circle 5" in diameter.
the robot has to sense dis gray circle and indicate dat it had reached a point either thro light or sound n den it has to move on n track d line.
the line will be a continuous one.black line on white surface.
it has to reach all d points in d arena and cum back to the starting point.

i hav two 150rpm & two 300rpm dc motors with me.
wich one will be suitable?
and cud u pls provide me sum links 4 the circuit diagram...
i hav to start frm d scrap n so i require so much of assistance.
plz also tel me abt programming in a microcontroller and a sample program.
wat sud i do 2 make my robot sense dat 5" grey circle n den cum out of it n sense the correct path....

please help me...