44 - Header (PAK File 2.01 (c) Black Cactus Games Limited)
4 - Unknown
4 - Directory Offset
4 - Directory Length

X - File Data

4 - Number Of Files

// for each file
  4 - File Offset
  4 - Offset To Next File
  4 - File Size
  4 - Unknown (Hash?)
  4 - File Type ID?

// for each directory {
  // NOTE: The next 3 fields don't appear in the first directory!
  4 - Number Of Sub-Directories In This Directory
  1 - Directory name Length [*2 for unicode]
  X - Directory name (unicode text - 2-bytes per letter)
  4 - Number Of Files In Directory (not including sub-directories)

  // for each file in the directory {
    4 - File ID (incremental, starting from 0)
    8 - Unknown
    1 - Filename Length [*2 for unicode]
    X - Filename (unicode text - 2-bytes per letter)
    }

  // for each sub-directory in this directory {
    // REPEAT FROM "//for each directory"
    }

The filenames are stored as unicode text, which means that each character is stored as 2 bytes instead of 1. For ASCII text, it is sufficient to read only the first chartacter in each pair, as the second byte will be null