I endorse everything rsch says above, writing as the person who rigged the wrong cave on the SWCC trip this summer. In my defence the only person in the party who'd been there before didn't spot that we were at the wrong entrance. Make sure that you are in the very bottom of the depression - the wrong entrance is a big obvious one adjacent to a big flat area that you land on having followed the path. In the summer the 'continuation' of the path from the big flat area becomes very overgrown so it's easy to think you can go no further down. The correct entrance is right at the lowest point.
It's a fantastic trip. Having rigged most of it beforehand the through-trip took us 12hrs+. Of course the locals mostly do the through-trip as a pull-down but the layout of the pitches would, I think, make this a major hassle, with lots of opportunity for snagging - you'd definitely need a spare rope and then you've got to drag all the rope through with you. It's a long way and tackle bags are a right pain in the two hours of 'marmites' (pools), which as rsch says are rigged rather sketchily.
Routefinding: you can't really go wrong, there are frequent waymarks, although in the final section we ended up in chokes that didn't 'feel' right even though we were following markers, so I guess there are places where more than one alternative is marked.
I suspect there must be a rigging guide online somewhere but if you can track down a copy of the Grandes Travesias guide that will have more info.
One more thing; if one of your party says he's going ahead to fill his water bottle, make sure you have a firm plan for meeting up again.
