How to generate xubuntu rootfs used in downloadable demos

General question, how are you generating the Xubuntu root filesystem used in the demo SD Card images here?

Zynq & Altera SoC Quick Start Guide [Analog Devices Wiki] 

I am developing my own application for a Mini-ITX z100 platform w/ FMCOMMS4 using custom HDL and software. I'd like a full Linux desktop running on it ideally. I've tried the 12.11 Linaro rootfs mentioned in the link below, but had stability issues with it (possible I didn't do the updates properly though):

Linux with HDMI video output on the ZED, ZC702 and ZC706 boards [Analog Devices Wiki] 

However, I really like the Xubuntu (Xfce) desktop used in the demo designs. Minus a few issues I'm trying to resolve with audio, it is rock solid. So I'm just wondering how you generated it. I'm just looking for a more direct solution than downloading a full SD card image, blowing it up and salvaging the rootfs from it to get my desired desktop. Thanks.