I've only read up on it only some, so I can't answer in detail.
And i'm sure you've looked it up something, like http://support.microsoft.com/kb/92635
My take:
A temp file is used by a program while using that prog.
The location for temp and tmp can be moved to another drive.
Something like a ram disc would dump, @ power off, the contents of folders mirrored to the rd.
You can manually delete both temp and tmp files but some files may not be deleted if they are in current use by a prog.
All tmp and temp files can be deleted, but thiers an efficient way to do it.
Seems like windows has a setting that will empty those folders on power off.
Instead of looking for single temp files/folders...
Download Temp File Cleaner (TFC)
Double click on TFC.exe to run the program.
Click on Start button to begin cleaning process.
TFC will close all running programs, and it may ask you to restart computer.