virtualbox.org

So I have installed Debian 6 guest machine on a WinXP host and configured a bridged network connection for the guest. However, I can't access the Internet from the guest PC while the host's firewall is active (I use PrivateFirewall 7 btw), or connected to it for that matter. Although, I can still access the guest machine from the host (I use the guest as a web-server).

Of course, everything works perfectly when I disable the host's firewall (the guest PC gets full internet access and is open for internet connections).

I've read on this forum that this shouldn't happen with a bridged connection, so I'm at a loss here.

Things I've tried:
Checked the firewall's filters and set all processes related to VirtualBox to ALLOW
Checked my router's DHCP client list for the guest machine, but everything was in order (the guest's MAC was registered correctly)

Any help will be much appreciated.

To keep it simple:
Bridged mode is actually made by using a network driver that is installed at the NIC level, so "simply" allowing the processes will not work with antivirus/firewall as the real traffic would come from the kernel or other internal OS features and not directly from a program.
It will appear as if your VM is sending packets with the wrong IP, as the IP is defined in the guest, so the host is unaware of it.
That can easily be considered a security thread (and the border line with IP spoofing is very close here) and blocked by security software.

You should have a chat with the people of PrivateFirewall directly.

Could there be any other reason besides an wrong IP? I've checked the firewall's logs and it shows the correct local IP of the guest PC for blocked outgoing connections.

I've also manually assigned the guest's IP in the router (using the VM's MAC address).

There could be many reasons, but everything would be speculating on what actually triggerd the block in your firewall software.
You've established without doubt that the issue is only there when the firewall is active, so the rest is up to the PrivateFirewall support.