Exhaust before turbo?

hi, first of all some dumbass questions...

when people talk about cat-back exhausts, does this actually include a new cat, or is it just from the cat... back??! ok, now please someone correct me if i'm wrong, am I right that the exhaust manifold connects directly into the cat, or is this the downpipe?

anyway the reason I'm asking this is because I need an exhaust in preperation for a turbo, I picked up some great advice a couple of months back on this site and i just need a bit more help. From what i've told, i'm trying to go for a full 3" bore system. would this normally include a cat? if not, would my standard one be too restrictive? also, would a turbo come with it's own manifold which would then connect straight onto my new 3" piping, are there any more restrictions to worry about?

ok, now which exhaust do i get!!? I'm in the UK so i'm more limited than you guys and I'm finding it hard to find an exhaust system that has 3" piping all the way through. I can get DC Sports exhausts so do they do anything suitable?

Sorry for all the questions but once I understand what i'm talking about my posts will be a lot shorter!

thanks,

Bert