Thanks mamba,
finally I managed to install the xoops-2.5.1a on XAMPP (Ubuntu 11.04)
here is the folder permission that I have to make to install it:
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/uploads
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/uploads/avatars
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/uploads/files
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/uploads/images
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/uploads/ranks
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/uploads/smilies
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/mainfile.php
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/xoops_data/caches
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/xoops_data/caches/xoops_cache
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/xoops_data/caches/smarty_cache
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/xoops_data/caches/smarty_compile
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/xoops_data/configs
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/xoops_data/data/secure.dist.php
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/xoops_data/data/secure.php
sudo chmod 777 /opt/lampp/htdocs/www/xoops-2.5.1a/htdocs/include/license.php
hope it will save some time for other XAMPP users.
Also here is a good explanation on
chmod command
happy Xooping...
Deepak