G/A,
There is no difference between public and private messages (AIM) with the CFMU internet application (CIA), it's the functionality is completely different, and therefore requires a licence to gain access.
The public application will give you the ANM/CRAM, Structured and free text FPL editors (directly checked by the automated system at IFPU), as well as any relevant messages issued by CMFU/FMD (AIM) and military airway activity (CDR's)
The private application gives access to such functions as slot management, delay analysis and 'envioroment' issues within CMFU and associated FMP's and ATC - basically it's for airline operator use only.
Hope this helps...
C.S.