What are you exactly looking for, a real racing bike or just something we call regular bike? The easiest option for the latter is probably the public transport bike rental greenline energysaving polar bear friendly bike thing (OV-fiets in Dutch), although I dunno if its possible to rent those bikes for multiple days.
Probably way too late, but maybe for next searchers: you can rent a road bike in Utrecht and several other dutch cities at http://www.rent-a-road-bike.com/