dll problems

Hi, i downloaded the php_oci8.dll and tried to load it with my php.ini file using the extension directive. But i always get the error message: PHP Fatal error: Unable to load dynamic library 'php_oci8.dll'. I get an error message for 'php_ftp.dll' and 'php_oracle.dll', too: The php_oracle.dll error message is different from the others: PHP Warning: Invalid library (maybe not a PHP library) .... So, wheres the problem. Iam sure that my extension_dir is configured right and that these are valid librarys. I tried diffrent releases of php4 but non of them works. I even get diffrent messages from 4.0.1. It accepts the php_ftp.dll, 4.0. does not. Hope someone can help me. THX ->Flo