A: There are several 
methods to do this. Here is one option.
  (* Is a drive a CD-ROM with MSCDEX driver installed *)
  function CDROMFN (drive : char) : boolean;
  var regs : registers;
  begin
    cdromfn := false;
    if swap(DosVersion) < $0200 then exit;
    drive := UpCase(drive);
    if (drive < 'A') or (drive > 'Z') then exit;
    FillChar (regs, SizeOf(regs), 0);
    regs.cx := ord(drive) - ord('A');
    regs.ax := $150B;
    Intr ($2F, regs);
    cdromfn := (regs.ax <> 0) and (regs.bx = $ADAD);
  end;  (* cdromfn *)
The other relevant $2F interrupt functions you can use are $1500,
$1501, and in particular $150D.