You might be looking for a faster, jazzy PC. But, have you ever thought what good things you can do with the old PC rather than dismantling it totally. I have some ideas. May be that can help you out. I would like to share this with you, guys.
Make it is Home Server: If you are running Windows on your PC, you can install FTP server software in your machine and use it up to transfer files between computers. Or otherwise, you can install GNU/ Linux on it and use it as storage server.
Make it a browsing workstation: You can plug in to your old PC to internet and use it just as a browser. Your guest can use it when they come to your home. Or you can give it to your kids for their use with some kind of Firewall protection. They may need to access fastest and latest PC of yours.
Use it for your home security: You can buy a few webcams and USB splitter. Put the webcams at different location in and around your home. Connect the cams with your PC. Whenever you are away from home for vacation, you use the stream from the cam to the internet to keep track of things back home.
Use it as a TV: You can hook up a TV tuner card and use it as a TV. Browse your favorite channel without spending a few hundred bucks to buy another TV set. You can hook up your TV to your old computer by using Windows XP Media and watch all of the movies.
Donate PC: You can also donate your PC at some charitable institution or to a school in your district. Some PC makers like Gateway have Charity Programs.
Use it as a learning tool for Hardware Assembly: You can take things apart from your old PC. You can practise how to connect RAM modules or remove Hard Disk. Learn how the CPU is connected with the Motherboard.
Upgrade your Old PC: If you dont require any high end PC immediately, you can upgrade your old PC. Put some new memory, hard disk or even a new video card. That may do your job for a while without any upfront investment for new PC.
Use it as a Play Station: The hardware of Video gaming machine decays faster than PC. NES, Sega Genesis, Super Nintendo, and lots of MAME games should work well with older PC. In other word, you can use it as a gaming machine.
Sell it at eBay: You may be wondering that there are many people who are looking for used computer parts. You may get very little cash reward, but it is better than nothing.
Trade it in: Some dealers give you discount if you trade in your old PC and buy a new PC. Just make the PC look nice when you visit the dealer.