They are actually quite easy, and you might have gotten a quicker response on the Premiere Pro forum. It is time to expand the number of people you know, since the ones you already know, do not know everything you want to know.
Place the long clip in the source window, then set the in/out markers, and grab the middle of the picture and drag it to the Project Window. Then immediately rename the new clip in the Project Window, since it will have the same name as the original. Change the in/out settings and drag the next section to the Project Window and rename. Keep doing this as often as necessary to get all of the smaller clips into the Project Window and renamed using descriptive names.
The problem is that it references the original clip, and is not limited to just the in/out settings. But they can easily be used as subclips. Just be aware that they are not locked down to just the area you selected. They can easily be expanded, but this should not cause a problem once you know the deal.
If you really want to delete the original clip, and make true subclips, use the Project Manager to trim the project. That will create all new clips, and you can delete the original. Thos new clips should be just the selection plus the designated handles.
Steven
Adobe Premiere Pro 1.5 / After Effects 6.5 Pro https://www.stevengotz.com
Learning Adobe Premiere Pro 1.5 https://www.lynda.com
Contributing Writer, PeachPit Press, Visual QuickPro Guide, Premiere Pro 1.5