If you have more fonts than you really use, you're wasting precious disk space. There you'll find a list of all your installed fonts. Double-click a font's name to get copyright info and file size, as well as an example of what the font looks like at sizes up to 72 points. Delete any unnecessary fonts, and you'll free up a bunch of disk space. The Windows Registry is a database of all your system's settings and software.
Real life is less tidy.
System crashes, buggy uninstall programs, and plain old bad luck can clutter your Registry, leaving it full of improper associations, bogus lists of installed programs, and all sorts of other junk that can slow down and even crash your operating system. This download hunts down and removes bogus Registry entries automatically. It can also reverse any changes you make and restore your previous Registry if something goes wrong. Make a routine of cleaning the Registry, and Windows 98 will run faster and be more reliable. Not intended to be a substitute for professional advice.