You might come across numerous posts which tell you how to share files between windows and linux. This is one of them but in quick and easy steps.
1. Install samba
sudo apt-get install samba
2. Edit samba
gksudo gedit /etc/samba/smb.conf
3. Add the required details
workgroup = Homegroup
usershare owner only = false
server string = %h server (Samba, Ubuntu)
usershare allow guests = yes
4. Restart samba
sudo service smbd restart
5. Go to the folder you want to share and right click on it. Select sharing options. Check the boxes for Share this Folder and Guest Access
6. Go to windows 7 PC , open File browser and right click on network. Click on Map Network Drive.
7. Now enter the ipaddress of the Ubuntu PC and the folder share name. Save the settings. eg. If your ip address is 192.168.1.3 and your foldername is Public, add your share like this \192.168.1.3Public
Thats it! Your shared folder from Ubuntu can be accessed from windows machine.