configuring the php.ini file

I have PHP on both a window and Linux box. If I wanted to enable Sybase from the php.ini for windows I would uncomment the "extension=php_sybase_ct.dll" line. But in Linux you don't use the dll but the so files. But inside of my extensions folder on the Linux box there is nothing. For were are all the so files, on the windows box the extensions folder is full of dlls. OR in Linux do you have to always recompile PHP to enable any new database support. Thanks, Mark.