How to go from Brussels to watch London Olympics

Hi,
Never been to London before. Can someone please advise how to go to London from Brussels to watch the olympics. Needless to say that I am looking for cheap options :-)
There is a train to London. Any car pooling (advisable?)?
* Should I buy the ticket to the last station?
* On which shop should I get down for Olympics?
* Do I need to use local public transport? If yes, what type of transport. Few details please.
* Can I buy the tickets there or I have to buy online only?
* Are tickets cheaper/same at the counter or online?
* How far are the sports venues? possible by public tranport from one venue to another?
* Where and how to find cheap accommodation for one night. Are the rates 2 or 3 times than usual?

Thanks in advance.