Meant to post this some time back..
If anyone is looking to hire bikes whilst on hols in Lanzarote, here's the place:
http://www.mountainbike-lanzarote.com/index_eng.html
Don;t be put off by the crap website I visited this place and they have a great selection of bikes, road and mtb, They had some really nice carbon Treks and Merida's, all sizes, incl a 42cm (hello Dena) one!
As well as the bikes they also had loads of shoes - mostly Sidi and loads of pedals both spd and spd-sl
Well established place, and in a handy place on the sea front