Int 2A Fn 7802  - Network - PC LAN Prog V1.31+ - Get Logged On User Name   [N]

   AX = 7802h
   ES:DI -> 8-byte buffer to be filled

Return: AL = 00h if no user logged on to Extended Services
   AL <> 00h if user logged on to Extended Services
       buffer at ES:DI filled with name, padded to 8 chars with blanks.