This is an application that will simulate how your XMB will look on your computer before actually compiling your RCO’s and flashing them to your PSP. This application will let you view your XMB and its icons, backgrounds and colours. This application is meant to help you preview your XMB without actually flashing it, and NOT to help you preview already created themes!! With that said this program doesn’t even read your Flash0 (Unless your using the File Flasher) and doesn’t need your PSP to run (Again unless you are using the File Flasher. This program will not read RCO’s or have any PRX support, it will read BMP images and will arrange them so they look just like your XMB.

http://forums.qj.net/f-psp-development-forum-11/t-release-pspxt-100-lite-105605.html