This number is critical and you have to show it to get your ticket. They do not seem to have any way of referencing a reservation by name. You show your number at the ticket counter and then get your ticket.

I hope this works out for you!!!!

ok... what if I bought a ticket that says I can enter the palace at 6pm? does that mean I cannot enter the grounds before 2pm (morning cutoff). I wanted to go early, but that time is all that was left... thanks!

The best bit of advice I got about visiting the Alhambra was to get there early. Try and get a ticket for as soon as it opens, 8.30. I think it actually starts at 0900. It´s relatively quiet then, and not too hot. Check your entry time for the Nasrid Palaces,I think you have a half hour slot, if you miss it, tough! We shall be going in May again, and I intend doing the day and night visits. The evening visit, 10-11.30 is for the Palaces only.
Some useful stuff here, http://www.vivagranada.com/alhambratickets.htm and of the Alhabra itself,
http://www.vivagranada.com/alhambra/index.htm

Frank