Sadly I cannot afford the price now. I’ve already bought the developer license and I hope I will be able to use it in a kernel mode solution. I just need a start point, an example using winpkfilter in kernel mode or a way to avoid the overhead passing packets to user mode.
If you have kernel mode expirience then using IOCTL interface from the kernel mode should not be a problem for you. Otherwise, it may appear even more then difficult. You will have to create two drivers (SYS for NT/2000/XP/2003 and VxD for Windows 9x/ME, please refer relative DDKs for the details).
If it looks too difficult then you should try to optimize user-mode packet processing or upgrade (upgrade fee is 2000USD) to Source Code license(in this case you also won’t avoid kernel mode development, but you will be able to create cross-platform packet processing code using ready WinpkFilter interfaces).