Me he encontrado este ejemplo, lo he probado y funciona:
Código Delphi
[-]
function VarArrayFromString(const S: String): Variant;
begin
Result := Unassigned;
if S <> '' then
begin
Result := VarArrayCreate([0, Length(S) - 1], varByte);
Move(Pointer(S)^, VarArrayLock(Result)^, Length(S));
VarArrayUnlock(Result);
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
PostData: OleVariant;
Headers: OleVariant;
begin
PostData := VarArrayFromString('campo1=valor1&campo2=valor2');
Headers := 'Content-Type: application/x-www-form-urlencoded'#13#10;
Browser.Navigate('http://tu/pagina/web.html', EmptyParam, EmptyParam, PostData, Headers);
end;
// Saludos