You can using this bit of Javascript which you can put in your $$HTMLHead field:
<script language="javascript:> function showHelp() { var helpURL = "/[dbPath]/www-help/[keyName]"; helpWindow = windowOpener( helpURL,"helpWindow"); } </script>
<input type=button value="Help" onClick="showHelp()" >
where [dbPath] is a computed for display field with the following:
db1 := @Subset(@DbName; -1); db2 := @ReplaceSubstring(db1; " "; "+" ); @ReplaceSubstring(db2; "\\"; "/" )
and keyName is a computed for display field that resolves to a document name in the help view.