Online help for MS Windows - most commands will give help when run with /? or -? (COMMAND /? or COMMAND -?)

GUI Help is available from START - Help or by running the help files directly:

C:\WINDOWS\help\ntcmds.chm
C:\WINDOWS\help\ntdef.chm
C:\WINDOWS\help\ntchowto.chm
C:\WINDOWS\help\nthelp.chm
C:\WINDOWS\help\ntshared.chm

Syntax
      WINHELP [options] helpfile.hlp

      WINHLP32.exe [options] helpFile

In XP:    C:\WINDOWS\PCHealth\HelpCtr\Binaries\HelpCtr.exe

options:

-H    show help about help

-G[n] Build a .gid file and quit,
      If a number is specified, it determines which extensible tab to
      display by default the first time the help file is opened.
      A value of 1 would be the first tab beyond the Find tab.
      This command cannot be used with -S.

-S    Create a .gid file without showing an animated icon. 
      Cannot be used with -G. (winhlp32 only)

-W window 
      Specify the window for displaying the topic.
      This command cannot be used with -P.

-P    Show the topic in a pop-up window. 
      This command cannot be used with -W. 
      You must use the -P switch in combination with the 
      -N (context number) or -I (topic ID) switch.

-N contextNum | -I topicID
      Specify the topic to open using either a topic number, 
      (defined in the [MAP] section of the HPJ file.)
      or a topic ID string 
      (# footnote in the topic).

-K keyword 
      Specify the topic to open using a keyword.
      This command cannot be used with -N or -I.