a question

Hello, I have installed PEAR on my computer. I tried to use the command: pear install Net_DNS, but failed. The message is :pear/Net_DNS requires PHP extension "mhash". I checked the php.ini and found the mhash have already included in the extension. So I don't what's the problem. How can I solve the problem. Could you help? Thanks! regards Crystal This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.