Also try out DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver()); instead of Class.forName()...
This is generally a bad idea. It ties your implementation to an oracle database. You should only need to explicitly refer to the Oracle driver if you are planning to use some of its proprietory functionality. You also know the driver being registered is not the issue, because if the DriverManager could not find a driver to service the url you provide it would tell you.
Vista, unlike previous Microsoft OSs, comes with a firewall which is by default turned on. You might want to check this is not what is blocking your connection.
Cna you connect via SQLPlus? Can you connect with any of the other developer tools provided with your install?