I learnt from this WebmasterWorld forum posting that on Windows XP, the file-path for the Safari cache is something like this:
C:\Document and Settings\[username]\Local Settings\Application Data\Apple Computer\Safari
The cache file is named Cache.db - it's a .db file in the SQLite format.
In Windows Vista, the path of the Cache.db is C:\Users\
As explained in that thread, files like images are stored in Blob format within Cache.db file. These can be viewed with a tool like SQLite Maestro which includes a BLOB Viewer.
To retrieve files from the cache in Firefox type about:cache in the Firefox address bar.
In the page that opens up, click on the “List Cache Entries” link of Disk cache device section. This is where large files like Flash files are cached.
On a related note, I got to know from a recent experience that Google may not store images of the pages that it caches nor does the Wayback Machine archive every website.