MAC frame size

Hi people :

I´ve been writing a VB application that comunicates with a Cisco router using UDP.
The Cisco router complies with 802.3, so min¡mun MAC frame size must be 64 bytes.
If I need to send a 4 bytes payload from the VB application to the Cisco router, the MAC frame size becomes 4 bytes payload + 8 bytes UDP header + 20 bytes IP header + 14 bytes MAC header + 4 bytes MAC FCS = 50 bytes
This frame is discarded by the Cisco router because it´s considered a "runt" frame as has less than the minimun 64 bytes frame.
I´ve seen that UNIX servers add a MAC Trailer (fill in bytes after usefull payload) to fullfill the 64 bytes minimun frame size.
The question is how can I configure in the Win2K server and/or VB app. to send MAC frames of the requiered size.

In the case of a packet sent from the Cisco router to the Win2K server and/or VB app. (opposite direction), if the payload has 4 bytes, the router adds also a MAC trailer with zeros to reach to the 64 bytes minimun MAC frame size.

It seems that the padding (adding filling bytes to get the minimun frame size) is done by the NIC.
I need to sniff the dialog directly in the physical link