[Razor12911]

You have to make a label, a timer and do some calculations.

for example if using Inno Setup Enhanced Edition

var
Timer: TTimer;
PGPC: TLabel;

procedure PBTimer(Sender: TObject);
begin
if WizardForm.ProgressGauge.Max <> 0 then
PGPC.Caption:= IntToStr((WizardForm.ProgressGauge.Position * 100) div WizardForm.ProgressGauge.Max) + '%';
end;

procedure InitializeWizard;
begin
PGPC:= TLabel.Create(WizardForm);
with PGPC do begin
SetBounds(Left,Top,Width,Height);
Parent:=WizardForm;
end;
Timer:=TTimer.Create(WizardForm);
with Timer do begin
OnTimer:=@PBTimer;
Interval:=500;
Enabled:=True;
end;
end;

Use Curpage to show and hide label.