There is a great new mini computer called Raspberry pi developed as a experimental/educational computer that has blown away in sales with more than 1 000 000 units sold, Google donated 15000 unit for UK schools recently. In the autumn of 2012 a new model was released with 512mb memory making this a great product to build a media center on. My installation is based on Raspbmc a ready to run distro based on Debian and XMBC. What do you need besides the Raspberry pi 512mb model and a microsub powersupply (This need to be a high power model).
You also need a SD card, I would recommend a 16GB Class 10 card with 30mb/s read speed. This will make your installation and a fast boot time.
When you have all things time to get started.
Download the windows installer for Raspbmc
Accept the license agreement and select you SDCard in the listbox above, make sure you select right device because the installer will wipe the device.
When this is done, Add your SD Card to the Raspberry, ethernet cable with internet access and hdmi or RCA video. Time to boot up for the first time.
And after 5-15 minutes the XMB will boot up
Add your video folder by clicking on Files and add a video source and adding what scaper you want to use.
Enjoy, your new media center.