I've been researching the differences between 4.2 and 5.4. There is a fundemental difference in the two. In my research, I have not found anything that Cisco indicates that log files can be imported. Because ACS 5.4 has it's own robust logging and database viewing tools, I'm leaning towards no. But I cannot give a definitive answer on this, sorry. Just know that I've read for several hours, and have not seen anything that talks about the importation of logging files. You can import users, mac addresses, etc. This may be something someone knows and will post eventually; probably need to call "The Cisco" and get a quicker answer.