upgrade to hardy killed VirtualBox network access

[Edmund Ĺaugasson]

I upgraded Kubuntu 7.10 to 8.04 and VirtualBox 1.5.6 to 1.6.0 and also reinstalled guest additions 
in WinXP SP2 virtual machine but cannot acces to network anymore.

I use host interface so I have vbox0 and br0 (eth0+vbox0=br0) virtual network interfaces and also 
ifconfig shows them. I also use registered MAC address at my router. I fixed the new MAC address, so 
it corresponds as in router described but no success.

I also tried to remove whole network stack from WinXP using Device Manager window and then 
reinstalled it again but no success :(

Does anybody have an idea, what might be wrong?