The Upgrade Guide will give detailed instructions on how to upgrade, including using export/import for the upgrade. The Utilities Guide will give you details on the export and import utilities.
The basic idea of your migration is to precreate the Oracle database on the Solaris server. Then precreate any tablespaces you'll need. On the Windows server use exp to create a full database dump. FTP the dump file (in binary mode) to your Solaris server and then use imp to import the entire dump file.
This was first published in January 2007