One solution for your problem is

1. Open the export (dump) file using any textpad (if it too big don't use notepad). You can download textpad from net also.
2. Replace the string "TABLESPACE USERS" with your string "TABLESPACE yourtablespace".
3. Save the file
4. Now import the dump file into your database.

Note: If you are having database on Unix box, ftp it to NT box through Binary mode. Change the dump file and copy back to Unix box and import it.

By doing this way, your objects will import into your specified tablespace without any problem.

Thanks,