Now if you are lucky like me, you might have an old NES, sat around with tons of games like me, or you might not have had the chance to say experience the original Atari console. You might have lots of old game roms stored on a disk somewhere or even a usb stick or have downloaded from an emu rom site off the net (and no I won't be giving any sites due to the piracy technicality) however if you already own legally these roms and want to play them, I can show you how for about £40
Firstly you will need a £25 Raspberry Pi model B+ computer with 512mb of ram. A 8gb sd card, preferably class 10, a usb games console pad (I have a snes one but plenty of different ones out there), a power supply, hdmi lead and Ethernet/wifi connection to start with whilst setting up.
The easiest way is to download the card image from http://blog.petrockblock.com/download/retropie-project-image/ and follow the set up guide. Much of the hardworking has been taken out of this thanks to the image and with the recommended free software to burn this to sd card you have completed much of the setup quite quickly.
Once done plug into the Pi and boot up, go into the menu and edit the configuration s this is where you can program the usb controller for playing games etc. next exit all together and run raspi-config. Expand the file system, adjust the memory to 256mb and over click to 950mhz then reboot.
Once loaded again you will need to note the IP address. Once obtained, use a file transfer program like FileZilla and log into the Pi using username Pi and password raspberry. Go to Retropie, then click roms and then open up the folder for which game system your roms are for dragging them over from you computer to the Pi. Obviously I cannot tell you to download them or from where, just how to do the step after;)
Once all your games have saved you can unplug the Ethernet/wifi, if into your tv and reboot and once loaded open your game, you will see a message about the usb game controller and bingo you should be now playing one of your old games.
I have so far found amstrad games work, game boy but weird on a huge screen, nes, snes, master system, mega drive. But found n64, play station and anything after about 1998 cannot cope or will not load, but hey this is a retro games console not up to date console so suffices what I need it for and that's to play some classic games.
If you run into any problems then there is the raspberry Pi forums and also http://blog.petrockblock.com/ where there is a ton of info and walk through guides, next up will be to add the ability to run this through a adafruit Pi touchscreen then I'll have something special.