Installing Ubuntu on a ThinkPad X21
Because the X21 does not have room for a CDROM, one must plug it into the dock to perform a CD based install.
Using the Live CD for any of the Ubuntu versions listed above, I was able to get the Live CD to boot, but installing Ubuntu to the Harddrive would hang during loading of the usb-storage module. Looking at the logs, I received the famed "Maybe the USB cable is bad?" error message.
Using the Alternate CD, was able to install. At the installer's boot screen, F6 and enter a boot parameter of "debian-installer/probe/usb=false" (don't use quotes). Once you're in the text mode installation and have hit your first set of questions, press Alt+F2 to enter the BusyBox console, then find and delete (rm) "usb-storage.ko" from /lib/modules/2.6.*/ Then Alt+F1 to return to the install, and answer questions as normal. The install process should work fine from here on out, and booting into your fresh installation should go without a hitch.