Okay, so I've managed to sniff out some stuff without typing in the keyword filter at all (because I didn't realise you had to go into advanced mode), so it does work.  However, I have been trying to get some specific stuff and I have pasted a perfectly decent URL into the keyword filter but the 'Sniff Network' button remains totally inoperable.  Grey and dead.  Why?

Edit - Okay, for some reason, it was already doing a search without me touching the button so I clicked on 'stop search' and that made 'sniff network' available.  Now, however, there is absolutely zero coming up for a page I know very well has plenty of stuff to sniff....

2nd Edit - Still absolutely nothing coming up.  I read elsewhere on these forums that some helpers for others with similar problems were asking for the user's OS.  Mine is Windows XP.  I'm still trying all sorts and it's totally dead.  I wonder if clicking on 'clear all URLs shown' had any effect because I did this after coming across some clearly irrelevant and unwanted links.  Now it won't find anything.