PEAR package installer not working

PEAR package installer not working

OS: Win 7
XAMPP 1.7.7 portable
Windows command prompt
D: is the thumb drive
I'm trying to follow this post to fix PEAR settings.
When I enter pear config-show These values are returned.
PEAR executables directory bin_dir D:\path\to\xampp\php
User Configuration File Filename C:\Windows\pear.ini
System Configuration File Filename C:\Windows\pearsys.ini

There are no local PEAR files on my machine. When I enter:
pear config-set doc_dir D:\php\pear\docs
PEAR_Config::writeConfigFile fopen('C:\Windows\pear.ini','W') failed to
open stream: Permission denied)
How do I fix this?