Here is another fun-app of-sorts. Called Windows Info Box Editable, this free tool lets you change or edit the System Information easily to fool your friends.
Once you have downloaded this portable app, run its .exe file. To start editing the information, hit Enter.
In the box which opens, type the information you want changed. Click OK to change the next parameter.
This app let you change Windows edition, procesor name, RAM, System Type, Computer name, full computer name, full description and Workgroup.
Do note that I have not tried it, but you can download it from here. (UPDATE: Please read comments first)
You can also check out Windows 7 OEM Info Editor. It allows you to change OEM information like Manufacturer, Model, etc.
These apps will not let you change WEI, go here if you want to change Windows Experience Index artificially!