Title: Expand environment strings
If you have some environment variable (for example, '%WinDir%'), then you may use ExpandEnvironmentStrings function to get a real value of this variable.
procedure TForm1.Button1Click(Sender: TObject);
var
Str: array [0..255] of Char;
begin
if ExpandEnvironmentStrings(PChar(Edit1.Text), Str, 256)>0 then
Label1.Caption:=Str;
end;