anewdispensation - on Monday 7 Jan, I will start the Week 1 chat thread, in which I will post a link to the Spreadsheet of Fantabulousness. The lovely WillieWaggle has committed to creating this - which means she is going to be busier than me, based on the number of that have signed up!
All you need to do is enter your weight in the right column, and the SoF will do the rest. We enter weight in lbs, but there is a handy calculator on there to convert kilos to pounds, I think.
We mainly enter our weight on each Monday, but it's up to you which day you feel most comfortable with.
You will also find, on tabs at the bottom of the spreadsheet, some important information, like the rules, the list of allowed veg and other assorted stuff.
The spreadsheet is available via Google Docs, which means it is shared. If you are concerned about entering your actual weight, as some people don't want to, then you could always index it - so start at 100 and drop by 1 for every pound that you lose.
Generally what happens is that we all chat about our progress, raise any questions/concerns, share what food/recipes we're eating/using, and then I shout a lot at people when they cheat, and wave my Big Stick around willy nilly. 
And I start a new thread for each week. You'll find that they move so fast that the threads are usually in Active Convos - but if you're worried about losing them, you could always make them a Thread to Watch, or find it via Threads I'm On (assuming you've posted, obviously!)