本地安装时不能安装数据库

我用的是win2003 server,系统中安装了mysql5.0,在建立虚拟目录后进行安装到了第三步Set up database,提示错误
Database configuration
The following installation warning should be carefully reviewed:

Operations on Unicode strings are emulated on a best-effort basis. Install the PHP mbstring extension for improved Unicode support. (Currently using Unicode library Standard PHP)

Your web server does not appear to support any common database types. Check with your hosting provider to see if they offer any databases that Drupal supports.

在网上找PHP mbstring extension的问题,已经把php_mbstring.dll复制到C:\WINDOWS\system32下了,还是没有用,请大家帮忙!