I’ve had these questions myself, and been asked it by a few people: “How do I put my website pages on a Google Mini?” and “Can I install my own application on a Mini, e.g. my web app or webstats?”
The answer to both questions is: no, you cannot put your own web pages on the Mini (nor on the Google Search Appliance) and you can’t install your own applications either. They have a web based interface where you can change the look of their own pages somewhat, but beyond that you can’t do anything else. There’s no way of uploading your own pages on to the box, and there’s no way of installing your own applications.
Basically, these things are a plug-and-play box, they don’t like being fiddled with, and although that’s probably rather different from what most webmasters are used to, it does allow Google to be confident about how the box will work, and to avoid support costs covering people who install leaky web apps on to the server and then complain when it eventually crashes.