Bitnami already prepared everything to switch from Alias to virtualHost.
You can read everything about this here: http://wiki.bitnami.com/Components/Apache
In short: Change the Include line of your wordpress app in your \xampp\apache\conf\httpd.conf from httpd-prefix.conf to httpd-vhosts.conf
Then you should open the \xampp\apps\wordpress\conf\httpd-vhosts.conf file and change the lines Servername and ServerAlias to the domainname you want to use.
This domain name needs to be added to your Windows hosts file so that the domain gets resolved to your localhost ip 127.0.0.1
At the end restart your Apache.