One can play for a country one is a citizen of. Once you play for a country, you will only be able to represent that country in the future also, even if you have multiple citizenship. (there are exceptions when your nationality changes involuntarily, for example like in the former Yogoslavias case).

So England is stuck with Beckham :) I think he most likely will be selected to the team.

But I don't really know how this new nationality would work in UK's case. If you gain UK citizenship, which one of the four associations (England, Scotland, Wales, N-I) you will be eligible to play for? Maybe all of them? Or none? I don't even know how it works for the people originally from Britain. Atleast one could play for the team UK that will probably play in 2012 olympics :)

For some reason Almunia has never played for Spain, maybe he should have been given a chance at some point. But Spain has plenty of good keepers to choose from. If he becomes eligible to play for England, in my opinion he would be the very good choice for them (if we leave team chemistry and moral issues out of the picture).