Unable to install any extension using magento connect manager No Answer?

Try this may be its use full to you. It solved my problem.
Go to downloader/lib/Mage/Archive/Helper/File/Gz.php in your Magento directory
and replace

$this->_fileHandler = @gzopen($this->_filePath, $mode); 

with

$this->_fileHandler = @gzopen64($this->_filePath, $mode);

This is not fixing the problem, but if you look in your file system, navigate to -

downloader/.cache

you should see the package you downloaded as .tgz archive.

You can download this, extract, and then upload directly to your store.

I had the same problem.I searched for hours to this problem. I had a problem related to permission to the files and folders..I solved it as follows...

1. Go to "settings" tab of "Magento connect manager".
2. Then select "yes" for the field "Use custom permissions:"
3. Then save settings.
4. Now do the general process of installing extension in the "Extension" tab section.

Hope this helps...