My 5 year old Dell Optiplex 3.4 GHz P4 with 4G of RAM, dual DVI video card, tv tuner card and XP PRO is basically goofing off when performing any tasks I give it. Even when I have the tv on, a TurboCad 3D design open and a browser window open, there is no noticeable performance drop. You can buy a Dell Optiplex GX280 on Ebay for ~$100 -$150.
A Uniprocessor?....can’t be be worth much.
Try converting a full HD AVC video from a camera, down converting to 720p and putting it into a mkv file. You might schedule an overnight trip to occupy yourself.
I set my Core 2 Duo 2.4 GHz to encode some video and it’ll sit there for hours at 80-85% both cores. Just depends on how hard you push it.