Ah, good! If you've got that file, that's the most important thing.

Ok, deep breath here. Roughly speaking, the answer is "yes". If you would like a more precise answer to that question, please do take a few minutes and peruse the "updating the firmware" wiki:

http://wiki.maemo.org/Updating_the_firmware

This page will go into much more detail about exactly what the "firmware" consists of (for the N810 as well as for other Nokia tablets).

In short, you feed it into a "Software Updater" or "Flasher" program. The wiki above provides more information about this process, although you will need to skip over the parts that refer only to the N900...

What it contains is, essentially, what you are looking for: the code needed to reset the tablet to its initial state.

Yes. Hopefully, you'll be able to find it on skeiron.org, just like the .bin file. (I still can't seem to get through to skeiron.org myself). I think in one of your threads you mentioned that you have a Windows XP machine, so you'll probably want to get something called the "Software Update Wizard". Sorry I can't help you find it at the moment, as I can't see what is actually in the skeiron.org collection.