What happened to the old machine?
You can load Linux to it for free. Since linux needs so much less machine than Windows does, you will get a box at least as powerful as your new one (altho limited to other purposes).
Make a server out of it and you can replace all of your ISP needs for you, family, and friends. No more limits on webspace, email size, ftping. And host domains. And you can host games. And be useful as a beta tester. And you can provide hosting for peoples mods/maps.
Or if you are a programmer then you can play with the power side of it. Especially for really large text applications, databases, spreadsheets, etc.
Or you can automate your house. Lights, temperature, security, all of the things you have seen on any SciFi tv show. You can even give it voice control and give it a name or have it work as if its magical spells. If you want to consider that then visit
www.SmartHome.com (WARNING: hand the credit cards to someone else to hold before going there the first time if you have low self-control)