You need to duplicate the entire block, including the VirtualHost:
<VirtualHost wp1.localhost:80>
DocumentRoot "c:/xampp/htdocs/wp1"
ServerName wp1.localhost
<Directory "c:/xampp/htdocs/wp1">
Options Indexes FollowSymLinks
AllowOverride All
Order allow,deny
Allow from all
</Directory>
</VirtualHost>
<VirtualHost wp2.localhost:80>
DocumentRoot "c:/xampp/htdocs/wp2"
ServerName wp2.localhost
<Directory "c:/xampp/htdocs/wp2">
Options Indexes FollowSymLinks
AllowOverride All
Order allow,deny
Allow from all
</Directory>
</VirtualHost>
And then add the entries to your windows Hosts file (C:\WINDOWS\system32\drivers\etc\hosts):
i believe that you can either use different unique host name with same port 80 (<VirtualHost chat.com:80>, <VirtualHost blog.com:80>) or wildcard hostname with different unique port (<VirtualHost *:8000>, <VirtualHost *:8100>) in each virtual host section but not <VirtualHost *:80> for all....