I have a question,is it possible to render the image resolution 7500x5600 px in blender3d.I don’t know is it possible to render this with blender cycles.I have core i3 processor,4gb of ram,graphic card much older radeon hd2600 xt.If it is possible please let me know how much RAM memory I must have to render this huge image.Or maybe I need something else upgraded.My operating system win xp 64,and ubuntu 12.04 64 bits.Thanx in advance for your advices.
i rendered 4500x3000 on 64 bit system, but you image is 3x larger
only for storing this RGBA(float) image in RAM you need around 640 MB (= 7500x5600x4x4/1024/1024)
cycles need more ram for random numbers = +160 MB
and for RGB-screen image +160 MB
and i believe much more - if you enable passes, layers…
you need RAM for data, images…
if everything fail, you can render 3 parts (or more) of your image (2500x5600 + 2500x5600 + 2500x5600)
use camera shift to move rendering area without perspective change
and then combine all images with compositing
You couldn’t render it with the amd, even if cycles was fully functional with amd; the card is too old.
You can render an image that big, but it will take a while; I usually render 2560x1440, and occasionally 3500x2000 (ish). It takes time by cpu. Things you can do to reduce the time:
Turn down subsurf where looking at the image you cant tell.
Don’t render parts that are behind other parts - ie the side of a car facing away from the camera.
Careful use of lighting, glossy and glassy materials. Mixer shaders can also add to time required.
Ask for a volunteer to render it who has a good nvidia card. 
Folks are generous in the forum and willing to help, although not sure on that, but never know.