I take it you are refering to an audio file. (if midi then the answer will stil be yes) If you record audio into vst on the mac it will be saved as an AIFF file on the hard drive. If transfer this file from your hard drive onto the pc you can then import it into Cubase. I am not sure about VST 5 but i know that it is possible to transfer song files from a mac to a pc and vice verser using SX. ( a song file being what cubase creates if you click save in the file menu).
Hope this helps.
Keith