Well, everybody pays money 2 the EU and everybody recieves money, if you are a net payer or reciever depens on the difference....
Wrong. Countries like Spain, Portugal or Greece recieve more money then they give since they joined the union - compared to the "new" countries, those aren't poor at all. Over all, more countries are recieveres than givers which actually puts a lot of pressure on the richer countries and yes, with every new accession there is one more reciever, cause those countries are poorer than the rest.
Of course the system is not that simple as I put it here, but well.
You also have to keep in mind, that if I talk about a gap between the new countries and the old, I really mean it. Maybe a look at the GDP will help you to understand, I take my numbers from
http://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nominal)_per_capita
United States 42,000
Mexico 7,298
Germany 33,854
Poland 7,946
Romania 4,539
Bulgaria 3,459
Well, the US build a wall to keep Mexicans out while the EU did welcome Rumania and Bulgaria recently as members.
Ok, well, there's a lot more to it but now I really don't want to go further right now.