The best way is to update to 6.5 and you can open them via AMA. Then transcode selected material to the DNxHD flavor of your choice.
You can always create a separate startup drive, install the 30 day trial version of MC 6.5. Use it transcode all your footage, then go back to your 5.x version to edit.
If you go the import into 5 method, it is a painfully long import process.
Terence Curren
http://www.alphadogs.tv
http://www.digitalservicestation.com
Burbank,Ca