Want to install and link gd extension to PHP

On Linux / PHP, for one third party software (moregroupware), I need gd PHP extension. Initially I tried to uncomment the line in php.init as extension=php_gd2.dll but it did not work, i tried to find files for gd but only one file php_gd.h exists, so i tried with that extension=php_gd.h (I tried with php_gd.so too) But still nothing happened. The ext dir is as follows extension_dir=".\" Finally from internet I downloaded gd package and installed on server, but I do not know how to link to PHP. phpinfo() command shows config with apx2 and mysql, gd does not appear there. How to install gd and how to link to PHP ? can anybody help me please ? Thanks in advance, manisha