I have just helped one of my staff get a career break (albeit a 3 year sabbatical to move overseas with her husband). It is fairly simple provided that the support is there from the line manager and the desk officer. It is fairly simple with no great DW conventions to worry about (and there speaks an ex-ISS tutor). I think the process was started with a number of phone calls and then the submission of a Gen App (yuk I hate the bloody things!!!); more and more these days, since the loss of the formal letter (your obiedient Servant blah, blah, blah), routine letters and Gen Apps seem to be the acceptable norm. The process was handled pretty much by the guys at ACOS Manning who liaised with the branch sponsor etc.
My biggest piece of advice is to apply early as the whole process was, through no individual's fault, frustratingly slow.
Good luck; it is not that difficult and will certainly make your studies easier.
