Best way to travel in Spain

Get off of Eurorail and onto Renfe and Bahn. . You can't do Granada as a day trip from Seville. I think the train from Seville to Barcelona would have to go back through Madrid and take ten or twelve hours. Rework the itinerary or fly. Or skip Barcelona since it's on the far end of the stick, or take the flight home from there - - it depends on how much time you have.

As Ed says, Renfe is the site you should be using. And for just two or three trips a railpass probably doesn't make sense. You need to act quickly, though, since you might still manage to find some promo fares. You can do Cordoba as a day trip from Sevilla, but you can't do Granada as a day trip. You haven't given us any info about how many days you have all together, which would help us advise you.

Some more details about the information in the posts above. First, stay away from Eurail, or anything else that is a reseller. They do not list all trains, and mark up tickets for the trains they do sell. To find rail schedules throughout Europe, it's often easiest to use the Bahn (German rail) website, following Rick's tutorial: http://www.ricksteves.com/plan/tips/db_tips.htm This only has prices for trains that start or end in Germany. To find prices for trains in Spain, and to book them in advance to get significant discounts, you'll start with RENFE (Spanish rail), following this extensive tutorial: http://tinyurl.com/cu48wk5. Many people have trouble booking on RENFE. In that tutorial, they note that people can have more success with http://petrabax.com/renfe/, http://www.palacetours.com/renfe, or http://www.rumbo.es (the last won't hotlink for some reason). These are not quite as cheap as RENFE (they're resellers), but at least you can take advantage of the advance purchase discounts. Between Seville and Barcelona, you might want to fly. But, as said above, you will not want to try Granada as a daytrip from Seville, but will go from Seville to Granada and stay 1-2 nights to do it properly. If you will then need to get from Granada to Barcelona, you will most likely want to fly (Granada does not have AVE high speed service). To find flights, use Skyscanner: http://www.skyscanner.com/. Just like fast trains, flight prices go up substantially the closer you get to travel.

Kelly makes some good suggestion...slow down a bit and enjoy the places you visit. The AVE highspeed from Madrid to Sevilla is 2 1/2 hours, and about the same between Madrid and Barcelona. Purchase tickets in advance (non refunable) and save a lot. Tourist class is the way to go. There is a page on Tripadvisor which gives the way to navigate the site. Be sure to 'register' at the first opportunity on the site to make it easier.

Sevilla to Barcelona is 5 1/2 hours on the AVE if you take the 8:50 departure. It does go through Madrid but you do not have to change trains. Buy your tickets well in advance on Renfe ( or Petrabax or Rumbo.es if Renfe won't cooperate) to get the best prices.

We flew cheaply from Granada to Barcelona on Vueling airlines. Took 1.5 hours in the air which beats the 11 hour day or night train from Granada to Barcelona; total travel time to airport, being in airport, being in air, getting your bags (if you carry on) about roughly 5 hours, maybe 6. We were up by 5, cab by 6, at airport before 7am, flight by 9, in Barcelona before 11, in the city center by noon. We could have gotten to the airport a tad later as we had to wait 45 min for employees to arrive to check us into our flight. Fly into Madrid and out of Barcelona. Go the route of Madrid->Seville->Granada->Barcelona. Besides the train trip from Madrid to Sevilla, I found train and bus travel in Spain affordable. The train travel from Madrid to Sevilla on Renfee AVE was a reservation necessary train ride that can be cheap if you book ahead and commit to a time and date (the more cheap, the more non-refundable or changeable).
Hopefully you can go at a more relaxed pace. I would recommend 3-4 nights in Madrid (if 4, take a day trip; you have plenty of options). 2-3 nights in Sevilla (if 3, might be able to slip in a day trip to Cordoba, fitting it in when you are taking the AVE from Madrid to Sevilla). 2-3 nights in Granada (could easily be done in 2 nights but I really like to just roam around this cool place and chill out. You have to go to the Hamman Arab baths; bring a swim suit). 3-4 nights in Barcelona.