I'll see references to people like Lucien Goldmann or Gillian Rose, for two examples, and not have a clue what they're on about. Both in terms of the langauge and concepts used, and their historical contexts (don't really know anything about Luckaks or Adorno or whatever, or Hegel and Kant before that). So something that'll ease me into being about to understand this sort of thing.
I think what you are interested in could be (loosely) grouped into critical theory or continental philosophy.
I think the best place to start might be some of the general introductions to philosophy that people have mentioned in this thread. A New History of Western Philosophy by Anthony Kenny was mentioned by pickmans, and that is a very good place to start. Dr Furface mentioned A History of Western Philosophy by Bertrand Russell. You will find that useful, but it doesn't deal with any modern or contemporary philosophers (I can't remember who it ends with, someone like Henri Bergson?).
Also useful to you at this point would be some dictionaries. Penguin publish a
Dictionary of Philosophy, and for the kind of people you mention, like Lukacs or Adorno, there is also a
Dictionary of Critical Theory. These are not comprehensive, but they will be useful next time somebody mentions a term you don't know or understand. You can flick to the entry and get a basic idea of what it is about.
Also useful to you is
Squashed Philosophers. This is condensed (and in some cases extremely condensed) versions of a philosophical texts. It has a condensed version of many of the texts you might need to read. There is an entire canon of philosophical texts, but I don't think they are massively necessary unless you are an actual student of philosophy. You don't need to read and make notes on every single page of Leviathan by Thomas Hobbes, for example. You just need a general idea. Often this comes by a kind of osmosis, the more you read about one thing, the more you will pick up about how it relates to something else. It is all about making connections.
Squashed Philosophers is a condensed version of the works of many philosophers, and it useful for a general idea, but not really beyond that. Another website that you might find really useful is
The Stanford Encyclopedia of Philosophy. This is a bit like wikipedia, except it is curated by academics rather than members of the general public. The articles on there go into a lot of depth and deal with the complexities and subtleties of a philosophers thought.
It all depends how far you want to go with it all, though. There is no way you are going to understand Kant or Hegel without a proper understanding of most of western philosophy. There is just too much going on there.