Paypal Integration Problem (auto return)

Hi guys...
I juz wonder how can I auto return to specify URL after payment made? Currently buyer have to click on a link in paypal website after payment made.
below is my Paypal Payment Link:
https://www.paypal.com/cgi-bin/webscr?cmd=_xclick&business=xxx@gmail.com&undefined_quantity=1&item_name=S1001&amount=100.00&no_shipping=2&return=http://www.abc.com?success.aspx?ID=S1001&cancel_return=http://www.abc.com?error.aspx&currency_code=MYR&Ic=MY&bn=PP-BuyNowBF&rm=2
...