PaulS:
does this mean that i can't drive the Unipolar or Bipolar Motor with the power supply from the USB cable,because the text book was saying that i could overload the arduino
Your computer, not the Arduino, defines how much current it will supply via the USB cable. That limit is typically 500 milliAmps. That is generally nowhere near enough to power a stepper motor. 6 times that amount may not be enough.
is there any way out?
Proper planning in the future. Nothing now.
I have just finished implementing a Unipolar stepper motor circuit(L293 Driver) with my arduino UNO and a 12V DC Power supply and its working however my objective is to control five of these stepper motors Simultaneously,Can i connect them in parallel with out using the motorshield because i dont have it,if yes how?