For those who have problems programming on Windows using cheap equipment:
lowering the speed of the serial communication might help.
I have one of those cheap copied prolific devices, using 19200 baud I have very little problems, nothing an unplug and reinsert of the usb device won't solve.
also check for proper solderings.. a badly (cold) soldered connector can cause loads of problems.
Make sure RX and TX are correctly connected