yes, it's possible to install XAMPP on an USB-Stick. After downloading and extracting it on the USB Stick, start setup_xampp.bat (if it don't start automatically). There you will be ask, if you want to install it portable or not.
We don't provide any support via personal channels like PM, email, Skype, TeamViewer!
In the last couple years I've used XAMPP on the "portable app" (http://portableapps.com) and put XAMPP on a USB with the same directory structure ("/XAMPP") and clicked on the "xampp_start.exe".