Hm, After testing this over weekend I have descovered following:
No matter what I use, VNC, Terminal Service client or Folder browsing, network trafic dies after aprox 1 min. After another 1 min connection disconnects. When I connect again, I have the same thing, it works 1 min and then it just dies...

I'm searching microsoft MSDN and Google for tips on optimizing TCP/IP. Any ideas someone?