It would be a lot easier to stay within the same platform i.e.
either go unix to unix or nt to nt. I would only go from nt to unix if it was a once shot deal in your case. Did you mean that your export is 200GB? You could do the export, zip the file, ftp it to unix, do a gunzip, and then import. This will shrink the size of the file that you are sending via ftp.

You should do 5 exports, one for each schema. This should make each export file smaller. I think that there is a way to make exports span over multiple files, but I haven't done that myself. and make sure that you take the database out of archive log during the import, have plenty of rollback, and a large temp tablespace.