You would have to actually start the installation process to get to the custom installation--on other words, simply click Install. In OS 9, this is not a problem--it allows you to install just the modules you want without overwritng the core OS or erasing your files. But I've never had to reinstall OS X, so I'm not sure if you can do this or not without completely overwriting everything on your hard drive. You'd best ask Apple Tech support or ask the question on the OS X discussion groups on the Apple home page.