Don't worry about the Linux aspect, as zr0crsh says if your using the BT distro then a simple understanding will be fine. As long as you can move through a directory structure, chmod files, move files, copy files, manipulate network configs, etc then you shouldn't have a problem.
I'm 3 weeks into the course (having been on holiday for the last week) and can honestly say this course is superb. The videos are great and are mirrored exactly in the documentation, so if you haven't got access to a PC then you can at least read about the subject.
The exercises are well designed and stimulate exploration of the concepts being taught and the support is excellent - muts and/or ziplock are nearly always available through IRC to iron out any problems you have with the labs and then theres always the forums to revert to, though the forums aren't busy the info you find there is definitely worth noting and I think is fair to say, should be thought of as the FAQ for the course.
The bit I've found most difficult to get to grips with is the programming side, specifically bash scripting and python programming as I have very limited experience in that area - having said that Google is your friend here and there is plenty of sample code available for you to dissect and learn from - not hard but takes time.
Time is the one thing that always seems to be in short supply - I started this course thinking I would nail it inside a month but I reckon for your average Networking Joe with only limited pen testing experience and family commitments then 3 months would be more realistic to do it justice as (if your like me) you'll end up doing a lot of reading around the subject and experimenting with associated ideas. This has got to be a good thing as ultimately gaining the cert shows a thorough practical knowledge of the subject and not something that can be done via reading a few braindumps.
I'm finding the course extremely interesting and stimulating and would recommend it to anyone - if your currently sat on the fence deciding what to do - GO FOR IT !. You won't find a better value course anywhere and no I am in no way connected with the providers of the course I'm just very impressed.