Even though you can install XBMC on virtually anything, from an Android phone, iPhone (if jailbroken), Raspberry Pi device, and there are even Linux distributions that are made with sole purpose of running XBMC, I’ll again do the KISS thing and simply install it as an application on my Windows PC. You can go to www.xbmc.org and on the right hand side you will see a nice, large "Download" button that will help you to transfer the installation package to your PC.
When you transfer it (it's around 50MB at the time of writing) you simply go through setup like you would with any other piece of software. Defaults will work fine and when setup runs its course, you have the application itself installed and ready to run.
When you first run it, you will be presented with a nice, large user interface that is designed (also) for TV use. As such, you can completely disregard mouse and simply use your arrow keys to move around the interface. Enter will get you in a particular menu, while Backspace will go one level up. Full list of keyboard shortcuts can be found here. Of course, mouse will work just as well.
Now we will want to let XBMC know where media files are located. We will enter the "Videos" menu, then "Files" and finally "Add Videos..." section.
First we will add movies to the database. You will get an option to name the media files in the location. If you have more than one location where you store movies then name your location, so that it makes sense to you. I will simply call it "Movies". Then browse to the location where your movie files are. This can be on your PC or somewhere else on your network. Maybe another PC or on a NAS server. In my case it will be a local drive with Y: letter assigned to it.
When you locate the folder where your movies are stored, you confirm it. Then you will be able to let XBMC know, that the folder contains movies in the content selection. This allows XBMC to scan the folder and identify the movies and put up all sorts of nice things about them, such as title image, list of actors, summaries and so on. When you get asked if you want to refresh the info for all items in the path, answer "Yes".
Movies are added, so you need to add your TV series as well. Process is the same as before. Only difference is that you now you specify content as "TV Shows". When you're done you again answer affirmatively to the "refresh info" question. You should now have Movies and TV (or whatever you named them) in your list of libraries.
And that's it! You're done! After the scan of your files is finished and you back out of the menus, you will be able to see two new entries in the main screen. One will be "Movies" and other will be "TV Shows". If you move over them, you should already see what content XBMC was able to find and catalogue.
And if you enter the individual selection, you will be able to see your media files and start watching them.
This completes the initial XBMC posting. Sometime in the future you can look forward to information about remotes, subtitles, TV streaming and similar.
Enjoy this greatly,