To me, @YDayNo would seem to be the easiest to piece of info to build this one message a day code around. I would use the registry to store the @YDayNo of the last message viewed. The key\value HKCU\software\Local\messagenumber for NT and higher and use HKLM on Win9x computer.
Basically, if the value store in the registry is less than the current @YDayNo then show the message and then update the registry.
