I spent a month in southern spain in an immersion program. here's what i learned:
-weed is very well tolerated there. as long as you dont make a spectacle out of smoking and dont do it infront of churches or government buildings, nobody will bother you.
-its tough to come by bud for the most part. hash is popular there but its uber soapy. they smoke it out of hollowed-out cigarettes. be cautious when purchasing hash. like i said, its soapy.
-you wont see many pipes, more like huqqas/hookas. you can find glass in tourist spots. they are cheap,thin glass and a lot of times made out of clay.
-as for buying hash, if you know a local teenager, he or she can hook you up. you wont find men seeling it out of trenchcoats.
-they roll cigarettes there and you can usually carry around a joint and have it pass for a fug.
-alcohol is more popular than herb. they arent as passionate about it as we are. its just another thing, no big deal.

good luck and have fun! spain is phenomenal!