What is the WinRAR SFX header, and is it required? If so does it have a function?

If you are talking about the *.sfx files you use to make one; yes it is required. That has all the executable code for the sfx. So the gui that you see is in there, and the code to decompress is in there.

No I mean the ; The comment below contains... <--- that one, only I can't remember what its supposed to be...

it is only a line to remember you "that comment contains sfx script commands".

you can edit that line, i.e. ";BoardBabe was here" as long as it remains post ";".

lines starting with ";" are avoided, similar to "REM" under DOS.

Nice avatar Simon!

thanks buddy!