I have used Xamp before and inside your xamp folder, there should be a 'www' folder. thats where your files are to be placed. then you may goto http://127.0.0.1/filename.php. If you are using the software to create a web server for your site and no one can get to your site ex. http://your-ip-address, i reccomend you goto your apache folder, goto conf folder and find httpd. find #listen and under that if you dont see 127.0.0.1:80.. put 127.0.0.1:100. I use port 100 for my server because the isps dont allow me to use port 80.
on my side, using port 100 it would be http://127.0.0.1:100 then on the client side it would be http://my-ip-address:100. You can goto http://no-ip.org and do a port 80 redirection and set the port to 100 so your sub-domain can be http://you.no-ip.org then you can goto my.dot.tk and create a domain so it can be http://you.tk, unless you have a domain then you can forgett the above section.
I use a server software called appServ. In my opinion this is one of the best software to use, just beware, the mail(); function dont work, but with appServ, you get the latest version of apache, php5, mysql 5 and the latest version of phpmyadmin.
good luck and if you have any questions you may email me at amnva@charter.net and i will try to help you furthur.