You may extract the files by using the following command syntax:
java -jar arcturus_unpack.jar c:\path_to_your_arcturus\data.pak
If you want to specify the extraction directory, you may add --d=c:\your_destination_path.
Instead of using the unpacker here, you can use my enhanced GrfWiz, which can extract file names in desired encoding and to choose the type of files to be extracted.
My GrfWiz can be downloaded at http://starkwong.ivehost.net/arc/download/GrfWiz.zip
(With source, written in VB .NET and you need .NET Framework runtime 1.1)