PS, I had a week's road biking based in Alghero a couple of years ago. Flat and windy to the north and west, big and hilly everywhere else. I had a couple of stunning 100 milers, the best being down the coast to Boza then swinging inland in a big arc via Suni, Villanova and Olmedo.
There were a couple of bike shops in Alghero but I took my own anyway. This place does bike hire, probably low end, but they may know somewhere else.
www.cicloexpress.com
Or you could email this bloke
http://www.tripadvisor.com/members-forums/CentroStorico - he is based in Alghero and seems to know all about everything.
About 10 miles down the coast road to the south there is a steep road up to Villanova. If you can get straight up that, you are my hero: I had a couple of goes, but my log just says "Couldn't do this, even with a triple".

Think Hebden Bridge to Blackshaw Head with someone playing a blowtorch on your back.
Have a good trip.