The issue you described is the reason why I recommend a re-flash (at least for starters), unless you want to "roll up your sleeves and get dirty", so to speak. Re-flashing helps to ensure that you are "starting from a clean sheet of paper" and hence will help ensure a methodical approach to learning how to have NITDroid installed on your N900. I've had my share of the Guru Meditation error and with patience and experimentation and reading the threads here, was able to identify and understand (a) what causes it and (b) how to solve. A and B are very important, rather than just blindly following instructions that we don't understand. Because if so, there is no learning...only memorization.

EDIT: the "Guru Meditation" error is a common issue encountered by those new to those attempting to install NITDroid (with the old/manual steps) and forgetting a very important step. I'm not sure if re-installing with the Autoinstaller on top of an existing/prior manual installation solves it.

Note that the Autoinstaller is a script (i.e. a pre-progammed set of steps that will be done one after the other automatically). The Autoinstaller attempts to install specific versions of the NITDroid kernel and Image, so you might end up with two versions of NITDroid installed, which is "not a clean piece of paper" since I don't know if you have used the same versions of the NITDroid kernel that would also have been done by the Autoinstaller (sorry I'm not technical enough, I can only explain in layman's terms).

If you want to go the route of "rolling up sleeves and going dirty"...then I will no longer give specific steps for this will result to spoon-feeding. Now will be the time to visit the Grand NITDroid Thread to read and learn, because the "Guru Meditation" issue, as mentioned, was a common one encountered with the manual method of installation and hence, was encountered by many and they have posted to that thread already.