One reason why I have been resisting rooting my phone is because of the old way of rooting the HTC Desire HD. Best illustrated by the wiki on cyanogen mod. Essentially a many step process, of copying file, downgrade, copy file, reboot, and reboot.
Recently I have discovered Advanced Ace Hack Kit, basically these guys already automate everything as a 1 step process, if the firmware need to be downgrade it, will do it. But here is the big catch, it is a 32bit binary, and I installed a 64bit linux.
Thankfully mint, which essentially built on top of ubuntu(which in turn debian) have ia32-lib, which have 32bit version of library for 64bit OS. Just install it.
And read the manual, it is inside the package along with all the tools needed, unzip, and read the manual inside it. It covers everything, you need. There will be a quiz in the end ;-)