Trouble loading extensions under Win98

Hi, I'm trying to set up PHP 4.2.2 under Win98 (for command-line use). I'm trying to get it to load the IMAP extension, but I get the message: PHP Warning: Unable to load dynamic library 'c:\php\extensions\php_imap.dll' - A device attached to the system is not functioning. The path for the file is correct. I tried copying the DLLs in the php/dlls directory into the windows/system directory, but no change. I also get the same message for any other extensions I try to load. Any ideas?