>Can anybody help me. I have created a CHM fiel (help file) from which I would like to access by clicking a button in Excel. I have created a new button on the worksheet and when I click it I want to open my help file.

Take a look on HtmlHelp API function:

Const HH_DISPLAY_TOPIC = &H0
Const HH_HELP_CONTEXT = &HF
Declare Function HtmlHelp Lib "HHCtrl.ocx" Alias "HtmlHelpA" _
   (ByVal hwndCaller As Long, _
   ByVal pszFile As String, _
   ByVal uCommand As Long, _
   dwData As Any) As Long
Call HtmlHelp(0, "c:\help\Sample.chm", HH_DISPLAY_TOPIC, By Val "Topic1.htm")