First of all let me tell you that VHD files are "Virtual Hard Disk/Drive" files use to store operating systems and other stuff that can be carried form one computer to another and use anywhere without re-configuration. Thus it does not require any additional ISO files to configure or run, except the tool that can mount it as physical hard drive (Obviously to access the data in it).
Now as you are using oracle "Virtual Box" on your windows 7 and need to import VHD file in it, you need to provide a virtual machine that will treat this VHD file as physical hard drive. If you are having any operating system stored on it it will be booted automatically otherwise you need to install another operating system on virtual machine and attach this VHD to it as additional disk.
Now if you are having any OS on it then follow these steps:(Easy even without "Screen Shots")
1. Open virtual box
2. Create new machine with tool-bar button or from menu "machine=>New"
3. Type name of your operating system (already present on VHD file) and Identify the type (like windows XP, windows 7, Ububntu, etc.)
4. Select appropriate memory size
5. Now in hard drive selection menu choose option as "Use existing hard drive file" and give a path to your VHD file.
6. Now run your virtual machine and you will boot with your operating system.
If you are not having any OS on it then follow these steps:(Easy even without "Screen Shots")
1. Create a new virtual machine or seek for an existing one.
2. After creation of virtual machine, don't run it just go to settings of it. To go to settings use right click of your mouse.
3. Go to storage, add new "SATA CONTROLLER" and provide a path to your VHD file.
4. Now boot your machine.