Java is technology used to create interactive or animated web content, such as games or advanced financial applications. Java programs are downloaded automatically to your computer when you use them, and don’t usually require special installation. To run Java programs in Internet Explorer, special Java software needs to be installed and enabled. When the Java virtual machine is installed in Internet Explorer, Java is enabled by default and configured with safety settings at their highest. If you do not have Java installed, visit the Java.com website to download the free Java software.
First you need to download Java from here for vista.Now you need to install that’s it this will complete the java installation in vista
Once Java is installed, you can enable or disable it by following these steps to enable or disable Java in Internet Explorer
Open Internet Explorer and Click the Tools button, and then click Internet Options.
Click the Advanced tab.If Java is installed, there will be a Java section in the Settings list. To enable Java, select the option under Java. To disable Java, clear the option under Java. When you are finished, click OK.