There are only a few good choices for older hardware. Puppy is a good one to use. All of the specialty distro's are odd to some extent. Much of the things you might learn need to be thrown away on mainstream distro's.
Try slitaz, antix, dsl while you are at it. Your system is really at the edge of use.
The only other way I know of to learn on would be making a distro at SuseStudio and running it in a browser.