The following documents are mirrored from Ken Hancock

Nikon N90s Protocol
Nikon N90s Memory Map
N90s Protocol Example
Memo Holder Format
Nikon Datalink NKN - Format specification
Memo Holder Download Example
Strings used for translating various camera memory values
How to make you own MC-31 Adobe Acrobat document (Disclaimer: I haven't tried this one myself)