First, read the English article below.

This program allows you to create a virtual hard drive on your computer which you can then install Windows 7 on. You can then boot up Windows 7 in a window while you're running Windows 8.  Most users can leave the installation options at their defaults. You can download from Oracle VM VirtualBox virtualbox.org/  Oracle VM VirtualBox is a free program, though there are other options available as well. This method is great for getting quick access to Windows 7 without having to reboot, but graphic-intensive programs such as games will not perform well on the virtual machine. When using VirtualBox, you'll be creating a virtual drive out of the free space on your hard drive. You'll want to be able to dedicate at least enough space for the operating system to install and run properly (about 20 GB), more if you want to be able to install programs. Make sure that you are leaving enough space for Windows 8 programs and files as well. This will start the process for installing a new virtual operating system. You will be prompted to give the machine a name and select the operating system.  You can name the virtual machine anything, though simply naming it "Windows 7" might be the most convenient. Select "Microsoft Windows" as the type. Select "Windows 7 (32 bit)" or "Windows 7 (64 bit)" depending on the version you are installing. Your Windows installation disc will say which version it is. You cannot run a virtual 64-bit machine on a 32-bit computer. Click here for details on determine what version computer you have. You can only dedicate RAM from the physical amount installed on your computer. Windows 7 requires 1 GB (1024 MB) of RAM, and it is recommended that you allocate about half of your available RAM for good performance. Don't allocate all of your RAM, or your regular operating system will encounter errors when the virtual machine is running. This will start the process for creating a new virtual drive to install Windows 7 on. If you know you'll need the hard drive image file for other programs, you can choose... 

Now, please write a short abstract for it in Chinese. Abstract:
下载及安装Oracle VM VirtualBox。 确保你有足够的可用空间安装Windows 7。 点击VirtualBox窗口上方的“New”（新）按钮，开始安装新的虚拟操作系统。 输入虚拟机的基本信息。 给虚拟机分配内存量（RAM）。 选择“创建一个虚拟硬盘”（Create a virtual hard drive now），开始创建新的虚拟硬盘，以便安装Windows 7。 选择“VDI”作为硬盘文件类型。 选择“动态分配”（Dynamically allocated），或“固定大小”（Fixed size）的硬盘。 选择虚拟硬盘的位置。 设置硬盘大小或限制。 等待硬盘被创建。 下载Windows 7的ISO文件，或者将安装光碟插入DVD驱动器。 在VirtualBox主窗口选择新的虚拟机。 点击“存储”（Storage）页眉，打开“存储”菜单，选择安装光碟或ISO。 选择虚拟CD或DVD驱动器。 点击“属性”部分的小光碟按钮。 启动虚拟机。 按照提示随便按一个键，开始安装过程。 按照提示安装Windows 7。 启动虚拟机。