[Ferra]

function DriveExists(Drive:Byte):Boolean;
var
Drives: set of 0..25;
begin
integer(Drives):=GetLogicalDrives;
Result:=Drive in Drives
end;

function CheckDriveType(Drive: Byte): string;
var
DriveLetter: Char;
DriveType: UInt;
begin
DriveLetter:=Chr(Drive + $41);
DriveType:=GetDriveType(PChar(DriveLetter + ':\'));
case DriveType of
0: Result:='?';
1: Result:='Path does not exists';
DRIVE_REMOVABLE: Result:='Removable';
DRIVE_FIXED: Result:='Fixed';
DRIVE_REMOTE: Result:='Remote';
DRIVE_CDROM: Result:='CD_ROM';
DRIVE_RAMDISK: Result:='RAMDISK'
else
Result:='Unknown'
end
end;

Далее пишешь:

for i:=0 to 25 do
if DriveExists(i) then
...
CheckDriveType(i);
...