Author: Michael Britt 

Here is a method for retrieving a list of installed applications on a particular 
machine running a Windows OS.

Answer:

Start up Delphi. 
Select File | New Application. 
Add Registry to the uses of your new Unit. 
Place a TListBox (ListBox1) component on your form.
Place a TButton (Button1) in your form. 
Place the following code in the OnClick event of the Button1: 

1   procedure TForm1.Button1Click(Sender: TObject);
2   const
3     REGKEYAPPS = '\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall';
4   
5   var
6     reg: TRegistry;
7     List1: TStringList;
8     List2: TStringList;
9     j, n: integer;
10  
11  begin
12    reg := TRegistry.Create;
13    List1 := TStringList.Create;
14    List2 := TStringList.Create;
15  
16    {Load all the subkeys}
17    with reg do
18    begin
19      RootKey := HKEY_LOCAL_MACHINE;
20      OpenKey(REGKEYAPPS, false);
21      GetKeyNames(List1);
22    end;
23    {Load all the Value Names}
24    for j := 0 to List1.Count - 1 do
25    begin
26      reg.OpenKey(REGKEYAPPS + '' + List1.Strings[j], false);
27      reg.GetValueNames(List2);
28  
29      {We will show only if there is 'DisplayName'}
30      n := List2.IndexOf('DisplayName');
31      if (n <> -1) and
32        (List2.IndexOf('UninstallString') <> -1) then
33      begin
34        ListBox1.Items.Add(
35          (reg.ReadString(List2.Strings[n])));
36      end;
37    end;
38    List1.Free;
39    List2.Free;
40    reg.CloseKey;
41    reg.Destroy;
42  end;