I would like to learn how it works, how to navigate in it (run: "regedit"), how to remove bits of uninstalled programs that get left behind by hand, and how to remove undesirable aspects and add desirable aspects. In short, i want to learn how to interact with and use the windows registry.
After you uninstall a program you could use regedit and search for files to delete using name of program. It is much more efficient to use a 3rd party registry cleaner like JV-16 or other.
I like to use Ccleaner as it has registry cleaner plus other functions.
Registry entries are very program specific and any registry changes of this manner are best left to the programmers that created the application.
Windows code is not public domain so unless you have studied it in great depth or have Microsoft cert. then it is best to follow trusted advice when editing the registry. For more info on tweaking the windows registry go to:
http://www.pctools.com/guides/registry/
For basic description of Windows registry:
http://support.microsoft.com/kb/256986/
Check the Microsoft website for training and certification opportunities if you are serious in a career working with Microsoft products.
Another alternative would be to find "hacking" sites on the web. To start though I would first learn C++ programming and gain basic understanding of computer languages.