Your video card doesn't meet minimum requirements, from http://ubisoft-en.custhelp.com/app/a...m8yXzduSms%3D:
IL-2 Sturmovik: Cliffs of Dover system requirements
OPERATING SYSTEM: Windows® 7 / Vista SP2 / Windows XP SP3
PROCESSOR: Pentium® Dual-Core 2.0GHz or Athlon™ X2 3800+
(Intel Core i5 2.66GHz or AMD Phenom II X4 2.6GHz recommended)
RAM: 2GB (4GB recommended)
VIDEO CARD

irectX® 9.0c compliant, 512Mb Video Card (1GB DirectX® 10 recommended) - See supported List*
DIRECT X®: DirectX® 9.0c or DirectX® 10 (included on disc)
DVD-ROM DRIVE: 8X
SOUND CARD: DirectX 9.0c compatible
HARD DISK: 10GB
PERIPHERALS: Mouse, keyboard (joystick with throttle and rudder control recommended)
MULTIPLAY: Broadband connection with 128 kbps upstream or faster
*SUPPORTED VIDEO CARDS AT TIME OF RELEASE:
ATI® 4850/4870/5830/5850/5770/5870/6870/6950/6970
NVidia®: 8800/9800
/250/260/275/285/460/465/470/480
In the nVidia 2xx series, the last two digits have to be 50 or higher to meet minimum requirements.
By the way, even if you buy the "disk version" it is still the Steam version.