How does the Fidelius Charm work?

[caliburncy at yahoo.com]

No: HPFGUIDX 23142

This is another thing on my list for the Lexicon, and I would 
therefore like to get some feedback on it.  No use bothering the 
webmaster with stuff that could be readily explained (and perhaps has 
been discussed and dismissed already).

Fudge describes the Fidelius Charm as "the magical concealment of a 
secret inside a single, living soul."  More importantly, he says that 
the information "is henceforth impossible to find, unless of course, 
the Secret-Keeper chooses to divulge it." (PA10)  Yet Hagrid and 
Sirius both were able to find Lily and James hiding place without 
asking Peter, the Secret-Keeper.  Sirius says in PA19 that he went to 
check up on Peter, but after not finding him there and seeing no sign 
of a struggle he "set out for [Harry's] parents' house straight away." 
 What?  He talks like he knew where to go, but he couldn't have.  
Neither could Hagrid have known.  After the Fidelius Charm was 
performed the only way to find James and Lily was supposed to be via 
Peter's knowledge.  One might argue that Hagrid and Sirius could have 
tracked down the rumors of deaths occurring in Godric's Hollow and 
found them that way.  But Fudge's statement that "You-Know-Who could 
search the village where James and Lily were staying for years and 
never find them, not even if he had his nose pressed against their 
sitting room window" seems to imply that this would not work. (PA10)  
Clearly there is something that has been left out or not properly 
explained regarding the way the Fidelius Charm works.  Perhaps the 
'nose against the window' bit only applied to people seeking out the 
Potters with malevolent intent.  Perhaps the Fidelius Charm ceased to 
function when James and Lily died.  Neither of these explanations 
seems entirely satisfactory to me.  I'm not saying this is the key to 
some greater mystery, it strikes more as a basic inconsistency to me, 
but nevertheless it is curious.

Help me out here please.  Thanks!
-Luke