Mounting a pannier rack on a Trek road bike

I've just gotten into a uni course and am back to bicycle commuting.
With my laptop and in particular the big steel U lock my bag is just
killing my back, so I think it may be time to splurge on a carrier.

The trouble is, my bike (a 2003 Trek 2300 road bike) has no holes as
far as I can see for screwing on a carrier, unlike the kerbside-
rescued mountain bike and my ancient (and extremely heavy) Repco,
which do have those holes.

Does this mean I can't use a carrier with my 2300 and would thus be
forced to ride one of my crappy bikes if I insist on panniers or are
there racks which will mount without needing to bolt into holes?

Travis