To use Shared Folders in Solaris, first Share a Folder from the Oracle VM VirtualBox Manager. Select your VM, then Settings > Shared Folders, and click the "Adds a new shared folder definition" icon (a folder with a plus sign). Add the folder. Example: C:\Users\me\Downloads. It gets shared as "Downloads".
Next, start (or restart) your Solaris VM.
Then login.
Open a Terminal
cd /mnt/sf_<share_name>
Example: cd /mnt/sf_Downloads
Voila, your folder contents from Windows 7 is now view-able in your Solaris VM.