why i can't load the gettext extension?

Hi, i'm trying to load the gettext extension for the IMP/HORDE webmail project. i've installed all in a single machine with Win2k pro-iis5 and php like exe (not dll). i've trie to uncomment the line corrispondent line in the php.ini file (extension=php_gettext.dll) but when i launch a default php page on IE, i receive the error "Unable to load dynamic library 'e:\Inetpub\php-4\extensions\php_gettext.dll'" 'i've controlled: the extension exist in the specified folder, the gnu_gettext.dll library exist in the "dlls" folder of php instal folder. so i don't know why the gettex extension not load. someone can help me? thank's in advance Giorgio