In Linux I use kissattach to create an ax.25 interface for serial port communication. With this, I'm able to send/receive Data to/from these ports via UDP/TCP sockets.
Now I need to set up the same thing in Windows 7, is there any similar Program?
If someone is interested.. I didn't find any useful program, so I solved this with a Virtual Machine. From Linux-VM I routed the ax.25 Ethernet packets to VM's Host only adapter and so to Windows PC. Maybe not the best solution, but it worked for me.