Just to clarify one thing, you don't have a "physical drive", you have a "virtual drive" of 25 GB allocated to your Win7.
Now, if you go to your VM Settings » Network » Adapter 1, most probably you'll see that the "Attached to" value is set to NAT (that's the default at least). This gives you quick and easy access to the internet (which is what most people want), but it doesn't give you access to the rest of your network.
There are several modes of network (the "Attached to" value) that you can choose from. For a quick overview, please read ch.
6.2. Introduction to networking modes and look at the table at the end (it's a page long, not that big), which gives you an quick look of what each mode can do.
In your case you should select "Bridged". Bridged will allow your guest to appear as just another PC on your host's network. The host, all the other network PCs, the internet and the guest can all communicate. The guest would default to getting an IP address from your host network's router. The host needs to be connected to an active network to allow guests to use Bridged. And if you ask yourself, why isn't that the default, the answer is security reasons. You may don't want to or you can't sometimes have your VM appear as a peer to your network.
Mind you although that if you select Bridged over a WiFi card that Bridged and wireless don't always play nice. It may or may not work. Some combinations of Routers/Access Points, WLAN cards and drivers work, some don't. See:
Bridging & Wifi - Supported hardware and add your experience.