Oracle 7.3 is not certified to run on either Windows NT or Windows Server 2003, so if you're not having problems with your database now, you may as soon as you migrate your operating system to Windows 2003. Have a look at the certification matrix.
What you might want to consider is migrating the Oracle 7.3 to 9i or 10g on a different server running Windows 2003. If you choose to use Oracle's export and import utilities to accomplish this, the basic steps are as follows:
- Create new database on the Windows 2003 server
- Export the existing Oracle 7.3 database
- FTP the dmp file to the Windows 2003 server
- Import into the newly created database
Migrating from Oracle 7.3 to 9i or 10g is a quite a change so you will want to test this migration thoroughly to ensure that the applications supported by the database still function as expected.