you cannot copy complete Cubase projects to Cubasis at the moment.
However, you can copy MIDI-files and Audio files (.wav, .mp3, .m4a, .ogg) between Cubase and Cubasis as you wish using iTunes or the WiFi-Server. Since Cubasis does not support VST, I would recommend to export your VST-instrument track as a MIDI-track and choose a “best-match” instrument in Cubasis.
We released a Cubase plugin that facilitates the import of Cubasis files (Cubasis Project Importer | Steinberg). Unfortunately, it is not compatible with Cubase Studio 5.
If you have any further questions, please let me know.