I don't know if you installed Oracle 7.3 as a server or as a client. If you chose server you would have been prompted to set up a sample database (30 M, if I remember correctly).

If you did not see this series of windows go by during installation I don't think that the sample db is there. Next step is to whack that installation and try again. During one of the first screens you need to select either custom install or db server install.

Hope that helps
dougc