new component and new module installation error

hi,
* JFolder::create: Could not create directory
* Warning! - Failed to move file

i am getting above error while i am trying to install new component and any new module

some body told me to check the file permissions. i checked them. all are in writable mode and i have gave them 775 permissions but it is not still working . i have one doubt to which folders and files i need to give the permissions and i am unable to solve this problem
and i am struggling to solve this problem from 15 days. To which file i have to make the modification to solve this problem
can i solve the problem by unzipping the files and placing them in required places through ftp tell me whether it is suitable process or not.