For LMDE: http://lxlinux.com/debian.html .Would the LXDE fans among us like me to post a tutorial on how to do this step by step?
For Xububtu 12.04: http://lxlinux.com/xubuntu.html .
LXDE on Mint 13 XFCE and regular Mint were slow and sluggish - lost interest in them very quickly. LXDE over Xubuntu 12.04 was better (faster and more stable) than Lubuntu, and is fully supported for 5 years. Also, Xubuntu comes with Firefox and Lubuntu with Chromium - a big plus for LXDE Xubuntu in my opinion. However, my pick is LMDE with a mostly LXDE desktop - see the guide linked above. It is very quick because it is free of the Ubuntu bloat that naturally occurs in a Ubuntu based system. LMDE is slow with updates, but not a big deal if your system is 100% reliable as set up.