host OS: Ubuntu 10.04 x86_64
guest OS: Windows 7 x64 ultimate with SP1 English version

Pre-work:
1, download & install virtualbox in ubuntu. Virtualbox for Linux. I use Ubuntu 10.04 LTS AMD64
2, download windows 7 image file: filename.iso

start:
1, open VB, create a new virtual machine, I change the file location to a device with ntfs filesystem, 30GB.
2, click setting. 
    system:
        chipset ICH9
        I/O APIC: enable
        EFI: disable
        hardware clock: disable
        PAE/NX: disable
        VT-x/AND-V: enable
        Nested Paging: disable
    display:
        3D acceleration: disable
        2D Video acceleration: disable
    storage:
        CD/DVD drive: IDE Primary, type PIIX4
        load filename.iso
    USB:
        USB controller: disable (enable after installing. If you do not disable it, a blur screen may appear. stop: 0x000007E)
3, click start, install windows 7, identical to installing on a real machine.
Enjoy!