Cheap Eurail Passes

I need a simple Eurail pass explaination.?
I am currently studying in Spain and after the semester, I will have ten days to travel Europe and I am looking for the cheapest way to do it. I was told about Eurail passes. How exactly do they work and would they be best suited for the situation? I have ten days and I would like to travel to Paris, Berlin, and possible Ireland/Greece/Switzerland. I dont have a ton of money since it will be the final week and a half of my trip but I was hoping to do the trip for under 750 or so.
If you only have 10 days to travel, Ireland/Greece may be difficult to do in addition to Paris and Berlin. Switzerland is much closer, thus probably the better choice for a 3rd destination, especially if you plan to go by train.
Rick Steves’ guide explains Eurail passes very thoroughly:
http://www.ricksteves.com/rail/
Eurail passes are generally not the cheapest way to travel. If you book tickets ahead of time on a local level (using the internet), you tend to get much better prices than you would with Eurail. The passes are only good for basic travel, and you still have to pay for some reservations, like if you want a sleeper cabin on an overnight train.
http://www.bahn.de/international/view/en/index.shtml
You should also note that the pass doesn’t work through the UK.
Budget flights are often cheaper (and faster) than train travel. If you use Ryanair, you could easily fly Paris-Dublin, then Dublin-Berlin in that time frame. The destinations vary by cities, so you have to look at their route maps:
http://www.ryanair.com/site/EN/dests.php?flash=chk
There are many budget airlines, like Easyjet and Bmibaby (UK based). If you check the Wikipedia articles for airports in the cities you are interested in, it will list destinations and airlines, including the budget ones that fly there.
Also check Momondo for cheap tickets:
http://momondo.com
The airports they use are usually outside the city a bit, Beauvais for example is over an hour outside Paris. However, there are always good transportation options (a shuttle bus downtown, €13 to Paris) so it’s not much of a hassle for the money you save.