Hook for node preload Is there any hook for when the node_load or node_load_multiple functions are called, but before they are actually loaded from the DB?

I need this because I want to cache my nodes before Drupal goes and queries the DB for them.
No there's no such hook I'm afraid (see the list of hooks for Drupal 7).

If you want caching that goes beyond the normal static page cache provided by node_load() then you might want to look at the Entity Cache module, which "puts core entities into Drupal's cache API.". Even if you don't end up using that module you can inspect the code to get some ideas for implementing your own caching system.