You can tell apache to 'listen' on ports other than 80.. - look in your httpd.conf for the Listen directive , eg
Listen 81
now you could add something like this... (NOTE - these are very slack permissions , just get it working first then tighten up a little

)
<VirtualHost 127.0.0.1:81>
ServerAdmin
whoot@yaks.com
DocumentRoot c:/new_docs
ServerName localhost
<Directory "c:/new_docs/">
Options All
AllowOverride none
Order allow,deny
Allow from all
</Directory>
</VirtualHost>
restart apache ! & nav to
http://localhost:81
you can do name based virtual hosts as well but thats a pain on win32 (as everyones system seems to have its own take on where and how the hostnames are resolved IME!)