Title: Show list of valid drives
Use GetLogicalDriveStrings function for solving of this problem. This function returns point to a string, which has such representing: c:\#0d:\#0#0.
procedure TForm1.Button1Click(Sender: TObject);
var
MyStr: PChar;
i, Length: Integer;
const
Size: Integer = 200;
begin
GetMem(MyStr, Size);
Length:=GetLogicalDriveStrings(Size, MyStr);
for i:=0 to Length-1 do
begin
if (MyStr[i]>='a')and(MyStr[i]<='z') then
Memo1.Lines.Add(MyStr[i]+':\');
end;
FreeMem(MyStr);
end;