To upgrade 9iAS to OAS 10g, you'll need to follow the upgrade guide for your platform. For the Solaris platform, here's where you'll find the Discoverer upgrade procedure:
All OAS 10g documentation for the Solaris platform can be found here: http://download-east.oracle.com/docs/cd/B10467_05/docs.htm.
As for possible, well, if Microsoft and Sun can agree to be friends, anything is possible! I would recommend keeping your Oracle support contract current just in case you run into problems along the way.
This was first published in April 2004