What is ETA?
If you're like me (lucky you), one of the things you have not kept up with in life is who hates whom in Spain. Amid the speculation that a separatist movement I've never heard of may have been responsible for Europe's second most deadly terrorist attack since WWII, I did a little quick research and found that the group has existed since about 1960:

"(ETA) wants to establish an independent socialist Basque state straddling northern Spain and the southern end of France's Atlantic coast. The Basques consider their culture distinct from those of their neighbours and speak a language unlike any other in Europe. The Basque language (called Euskara) is believed to predate the arrival of the Indo-European languages to the continent, of which French, Spanish, German, Icelandic, Welsh, Serbo-Croat and almost all others are the modern descendants. The Basque region... has historically been one of the richest in Spain."

Guardian's interactive guide to Basque Nationalism in the form of ETA is here. Leaders of the Basque Country (one of the 17 independent Spanish communities) have distanced themselves from ETA and seek independence, or at least greater autonomy through political means. But by my reading, they would seem to have little or no chance of success.

From the why-do-they-hate-the-United-States department? They're still a little touchy about our support for Franco during the 50s, as they had assumed independence would follow the end of the second World War. Most experts seem to think they are not responsible for the bombs on the 11th, but they are still suspected.