"I'm am using Access 97, so everything I say applies to that and maybe or maybe not 
other versions."

"The first byte of each page seems to be a type identifier, for instance, the 
first page in the mdb file is 0x00, which no other page seems to share."

"In Jet4, an additional four byte field was added.  It's purpose is currently
unknown."

"At some point in the file the page layout is apparently abandoned
though the very last 2K in the file again looks like a valid page.
The purpose of this non-paged region is so far unknown. Could be a
corrupt db as well.  My current thinking is that this area is
unallocated pages based on the GAM (global allocation map stored on
page 0x01)."

"Access (Jet) does not in general initialize pages to zero before writing them,
so the file will contains a lot of unititialized data.  This makes the task of
figuring out the format a bit more difficult than it otherwise would be."

"Each MDB database has a single definition page located at beginning of the file.
Not a lot is known about this page, and it is one of the least documented page
types.  However, it contains things like Jet version, encryption keys, and name
of the creating program."