help with zend objects and resources

Hi

I'm having problems with an extension I'm writing atm - basically, I
want to do the following in php:

$foo = myclass;
$foo->load("somefile");
$foo->save("somefile");

Now, I can form the load() method correctly within the module but can't
find any documentation on how to make the resource that it returns
persistent so that the save() method can access it.

I'm probably being really dumb here, but I've been staring at the screen
for a few hours and going slightly mad. If anybody can point me at the
relevant docs or just tell me how to do it, brilliant.

Cheers

--
Gareth Ardron