thanks all for ur replies.
Dainis: here is what I intend to do: using get_vector C/C++ routine, save the LAN ISR's address in some pointer and replace the address with that of my own made ISR using set_vector routine. Now whenever a packet would be received, my own ISR will be called in stead of window's. I will check the type field of the packet received and if it comes out to be of my interest, I will go on processing it. Otherwise, using the pointer pointing to the ISR of windows, I will simply call window's ISR to take care of the received packet/frame. This is all intended to be used on win2000 and XP.