I've just posted a reply on exactly the same subject on another thread so below is just a 'copy and paste' of that reply. That thread is called Full time job + Distance learning (HOW). Hope it helps.
I did distance learning whilst working full time and having two young children and had exactly the same fears as you've got. However, don't worry too much. Just do as much study as you can and don't worry about learning things in too much detail, Also don't worry about remembering it once you've moved on.
I say this because when you go on the brush up course at your school prior to taking the exams you will find that all of that forgotten stuff will come flooding back and you will do MOST of your learning there. The school will go through the whole sylabus and give you loads of feedback papers (ie loads of known/past actual exam questions). These brush up courses are hard work - all day in the classroon and then up 'till gone midnight studying but you will learn it all.
At the start of each of my two brush up's i didn't have a clue and would never have passed any of the exams but because of the quality of the courses i got 13 out 14 first time - and i'm fairly thick!!!
Good luck. The course notes are totally daunting but the actual exams are not that hard if you have a basic knowledge.