Hi,
To join (or general enquiries of) IMAC ring up Phil Goddard, his contact details are on the IMAC UK website... http://www.btinternet.com/~b.colclough/imacuk.htm
There are entry forms on this site too, the entry fee to the club is £10 and each competition is £8 for a one day comp or £12 for a two day comp.
Woodvale was one of the events from the IMAC UK calender, there is another one this weekend too!!
Have a look on the website as it does give you a good idea of what we do.
The 'Known' schedules are also up on the website, get to know these since these are what you'll be flying at the comps. You'll also need to fly a 'unknown' schedule at the comp which is given on the day at pilots briefing.
Everyone starts in Sportsman class and then if they acheive scores above a certain level, consistently they are offered promotion to the next class. In the UK there are only 3 classes(same as Europe i think), Sportsman, National & International.

I think this covers some of your questions...if your still intrested, the best way to learn about IMAC is to get involved!...hope to see you at some comps!

Hope this helps,
Rich