ShowHTMLDialog function creates a modal dialog box that displays HTML. To use ShowHTMLDialog, which is implemented in Mshtml.dll, you need to dynamically load and call this function by using the LoadLibrary and GetProcAddress functions.

unit psvHTMLDialog;

interface

uses
  Windows, SysUtils, Classes, ActiveX, URLMon;

procedure DisplayHTMLDialog(AMessage : string;
              Resizable : boolean=false;
              AHeight : integer = 100;
              AWidth  : integer = 100);

implementation

type
  TShowHTMLDialog = function(const hwndParent : HWND; const pmk : IMoniker;
      const pvarArgIn : Variant; const pchOptions : POleStr;
      var pvarArgOut : Variant ):HResult; stdcall;

procedure DisplayHTMLDialog(AMessage : string;
              Resizable : boolean=false;
              AHeight : integer = 100;
              AWidth  : integer = 100);

var
 URLStr : POleStr;
 pmk : IMoniker;
 InParam  : Variant;
 OutParam : Variant;
 Features : PWideChar;
 LibHandle : THandle;
 ShowHTMLDialog:TShowHTMLDialog;
 AParams : Widestring;

begin
  LibHandle := LoadLibrary('MSHTML.DLL');

  if LibHandle = 0 then
    Exit;

  @ShowHTMLDialog:=GetProcAddress(LibHandle,'ShowHTMLDialog');

  if not Assigned(ShowHTMLDialog) then
   Exit;

  URLStr:=StringToOleStr(AMessage);
  CreateURLMoniker(nil, URLStr,pmk);
  SysFreeString(URLStr);

  TVarData(InParam).VType := varOleStr;
  TVarData(InParam).VOleStr:=StringToOleStr('');

  if Resizable then
   AParams := 'resizable:yes;'
    else
      AParams := '';

  AParams := AParams + Format('dialogHeight:%d pt;',[AHeight]);

  AParams := AParams + Format('dialogWidth:%d pt;',[AWidth]);

  Features := PWideChar(AParams);
  ShowHTMLDialog(0, pmk, InParam, Features, OutParam);
  FreeLibrary(LibHandle);
end;

end.

More information about ShowHTMLDialog function you can find here