Prefetch and Temp?

Question

When these are typed in the start-run line what do they do?

Answer 1

Prefetch and Temp are not commands - they are directories.
(e.g. %systemroot%\prefetch)

Temp directories exist in a number of locations for different applications. As the name suggests, they are used to store files temporarily. However, some files are not deleted when they should be and these temp folders can therefore fill up. If you close all applications then it should be safe to delete any files in the temp folders.

The prefetch folder is an example of Windows trying to be clever.
The folder is used to speed up the loading of applications - XP will load programs that it thinks you need before you ask for them. For example, if you use Internet Explorer, Microsoft Word and Quake very frequently then XP will prefetch these applications on boot so that they seem to load very quickly.