>I need to associate BMP files with MS Paint programmatically. I have downloaded a Rick Strahl's registry class from the files. My question now is How do I use this to change the BMP file association?
>My second question -Where do I find how the registry is structured so I know where to put stuff?

Regedit.exe from the run box opens the registry editor.

As for file associations, these are stored in HK_Classes_Root. You can find the bmp extension in the top half of this hive, where it will be given a file class. The second half of the hive is a list of file classes and progids. Lookup the bmp file class down there, and modify the value in Shell/open/Command to point at the new program.

The windows way to do this is to use the "opens with" dialog to change the association. This dialog changes locations from version to version, so I can't tell you exactly how to do it...