lockfaen - try this:
N.I.E. (EX14) / RESIDENCIA (EX16)
This book describes the application process with examples of how to fill out the forms plus loads more useful information:
http://www.innoword.com/media/spain.html
Application Forms and the
Regulations Governing EU citizens in Spain document.
http://extranjeros.mtas.es/
For forms - Click: Modelos de Solictudes
http://www.mpt.es/servicios/extranjeria/modelos_oficiales_solicitudes.html
http://www9.mpt.es/servicios/extranjeria/ciudadanos_UE.html
Simona, no you cannot be fiscally resident in 2 EU countries cant speak for elsewhere but I doubt it - if you think about it is pretty impossible. (And yes I do understand you cant pay tax on say Uk Govt pensions in the Spain.)
Sounds like you are trying to beat the system - well good luck! Now governments are broke the rules are getting even tougher.