Andy,
There are many others on this Forum who are better qualified than I am to explain this but I'm not sure they will be posting here so this is my explanation.
Many years ago England and Australia played a game of Cricket - one of them won the game, not sure who, and for some reason they decided to burn the stumps (wooden poles that the bowler tries to knock down) and put the ashes in a jug. Each year since then the 2 nations have played for "The Ashes". The event has been happening for about 100 years or so and as far as I can tell the Auzzies normally take the jug home. Last year the match was played in England and the home team won. This year has been built up with much hipe and enthusiasm here in the UK with the hope of a follow-on victory.
The "Series" comprises 5 (or maybe 3) 5 day cricket matches (games). Yes, 5 days each game

- We are currently in the midst of game 1. The latest report from the BBC is as follows:
FIRST TEST, DAY THREE:
Australia 602-9 dec v England 99-5
Australia dismissed Kevin Pietersen and Andrew Flintoff in successive overs to leave England on the ropes in the first Ashes Test in Brisbane.
Pietersen had an early let-off when Stuart Clark failed to hold on to a miscued pull running back from mid-on.
But he was soon on his way after offering no stroke to a ball from Glenn McGrath and was given out lbw for 16.
Skipper Flintoff's innings lasted three balls as he was caught behind off Lee for a third-ball duck.
Another way to explain this is Australia 602, England 99 - not looking good for England at this point in time :?
Anyway, this will last for many weeks and at some point I am sure my English friends will chip in to explain in more detail.
Derek