Steps to create virtual hosts for a WordPress Multisite setup on a Xampp installation.

Xampp WP MS

Setup Xampp Virtual Hosts
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http://austinpassy.com/2012/setting-up-virtual-hosts-wordpress-multisite-with-xampp-on-windows-7/

All custom domain names must match the urls stored in the WordPress database from the General Settings page.

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XAMPP SETTINGS
File: /xampp/apache/conf/extra/httpd-vhosts.conf

Unhash:
NameVirtualHost *:80

Add:
<VirtualHost *:80>
    DocumentRoot "/xampp/htdocs"
    ServerName localhost
</VirtualHost>

<VirtualHost *:80>
    DocumentRoot "/xampp/htdocs/test/wp"
    ServerName wp.dev
    <Directory "/xampp/htdocs/test/wp">
        Options Indexes FollowSymLinks ExecCGI Includes
        Order allow,deny
        Allow from all
    </Directory>
</VirtualHost>

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WINDOWS SETTINGS
File : \Windows\System32\drivers\ets\hosts.conf

No wildcard subdomain (*.wp.dev) possible. Each subdomain requires its own line.
Add:
    127.0.0.1           wp.dev # Main dev localhost
	127.0.0.1       mmc.wp.dev # Subdomain 1