About Language. Part of the population speaks basic English so getting around at first is not that hard. This is more so in business and of course tourism. We are a country of immigrants, so people are very friendly and welcoming to foreigners. Your basic Spanish can ramp up in a couple of months if you take basic lessons. If you are really on a shoestring you can always place an ad offering "my English for your Castellano, conversation" ad on some hostel or hotel or just go to a pub! (this is trivial, everybody would like freebie conversation, this is a classic way for hooking up, too :) (BTW: the language is called Castellano, like the language you speak isn't called British but English; but it's the same thing.)
There are no safe parts of the country as a whole, it depends on the citi or town you pick. The largest city, Buenos Aires, 13 million, is mostly OK if you follow some basic rules (e.g. don't carry expensive watches or too much money, and stay in nice parts of the city.) If you have a big budget, you can live in isolation within the very expensive neighborhoods. But beware, it can get as fancy as you can imagine and your expenses get to Manhattan-life level. There are many areas in this city.
About security outside Buenos Aires, security is mostly very good. There are a few exceptions and again, in large cities you are OK as long as you stay within OK areas.
And even in the not that common case of mugging, say you leave a house party at a friend's place, it goes like this: "give me your money", "here you go", you give them your wallet with $200 and the guy leaves. You lost u$d 57, big deal, yawn. Just always carry something over 50 so they take it and leave.
Argentina is the 8th largest country in the world with an extremely varied geography. Have a look in Wikipedia. There is mountain, sea, jungle, prairie, desert, you name it. :) My advice is don't plan settling before checking out the options. ADSL 3Mbit is available on most big cities for $40-$70. The quality of the connection varies significantly.
Budget varies a lot. Touristy prices are crazy high, don't fall into that. Temporary rent is also 50% more expensive. In BA an OK-good flat with 1 bedroom will go for u$d 350-500/mo and u$d 70-100 more for bills. In other towns you can get a beautiful house for that money. It all depends. Transport is cheap, just try to have always coins with you (trust me on this one.) Groceries depend on how fancy you live, for my spartan lifestyle is about u$d 55-80/week. Clothes and shoes are somewhat expensive, bring them. Same for skiing equipment and stuff like that. Computer hardware is mostly cheap, fancy things are a bit more expensive, like laptops.
Something important: Don't use your foreign credit card. If you plan to stay, get a basic account with debit card (also, payments with local debit card get 4%+ refund from taxes.)
And don't get too literal on statistics, in particular of the CIA "Factbook." For example, they say it is an "intermediate" chance of getting disease here. This is only applicable for people who come already in extreme poverty.
For more info drop me an email.