One of the main things about IOW Josh is its the biggest event of its type (up to 5000 riders) in the Uk now, so much so that there are 'rallies within the the rally' just to find enough venues, campsites etc to house the hoardes who arrive.
http://www.iwight.com/just_visiting/events/majorevents/preview.aspx?eventId=593
I obviously wouldn't discourage you from going but I would say go to a smaller one first so you can see what goes on if you haven't been to a rally before? There are plenty before August so lots of choice.
http://www.bsra-uk.com/Events.htm
Hook up with a local club or two if you're new to club riding, and watch a few videos on YouTube too (IOW rally 2012 etc) to get a preview.
I often use the Red Kites SC listings to check whats on
http://www.redkites-sc.co.uk/?p=events
The listings in Scootering Magazine publish lots of events months in advance so you won't be short of options