Port forwarding is just that, forward data from it's original location on port X to the next distention on port Y (ports X and Y can be the same or different and can reside on the same system or a different one). Port forwarding is more for if you have a server behind a firewall/proxy and you want to 'forward' the traffic destined for port X to your server. If you have port forwarding enabled and nothing listening to that port on the other end, then nothing happens (as expected).
I have an exact setup like yours (Win7 host, *nix guest). To set it up to get them to 'talk' here's what you'll need to get setup:
On the Win7 host install a Windows Loopback Adapter (https://social.technet.microsoft.com/Forums/en-US/w7itpronetworking/thread/259c7ef2-3770-4212-8fca-c58936979851/) gives a decent enough description on how to do that.
Since the loopback adapter functions as kind of an 'emulated' NIC, you can use it just like any other NIC, so assign the IPv4 address to whatever you would like (I use 192.168.0.2 with a subnet mask of 255.255.255.0 for mine).
On your virtualbox machine settings, set the network adapter to 'Bridged' and set the interface to the 'Microsoft Loopback Adapter'. If you want 'internet' access to, you can setup a 2nd virtual NIC set to NAT (google 'network address translation' for more detail on what NAT is and is not).
Boot up your Ubuntu guest, set it's IP address to 192.168.0.X (X is anything but 2, 0, and 255) and the subnet mask to 255.255.255.0.
That's it, you can now talk between your guest and host. Once you have Samba installed and configured correctly on your guest, you can now browse to your guest from your host by going to 'start->run' then typing in \192.168.0.X\sharename (where X is the guest and 'sharename' is the share name you setup in your samba share).
Hope that gets you heading in the right direction
EDIT: Quick note on the loopback adapter. If you view its speed on the Win7 machine you'll see it says '10mb' (yes TEN megabit), this is a misnomer because loopbacks don't actually have a 'speed' associated with them, so Windows reports 10Mb in its place. The reality is that the 'speed' of your loopback will be as fast as VirtualBox, Windows, and Ubuntu can transfer data over that interface. So in all actuality it might honestly be closer to 100Mb or 1Gb or more, but just know that the 10Mb speed can be disregarded as the actual speed.