I've thought about it for a while and with the easy digital picture frame approach, there are basically two approaches to the electronics-
1- Replicate the graphics Metal would display in "real life". Treat the robot purely as a character.
2- Load him up with all kinds of cool snatcher related videos and sounds and treat the robot as a weird kind of Media Display device.
I'm first just going to do a picture, sound, and video media display kinda thing first which has a lot of cool possiblities.
I can just make one big video file of the game from a Youtube walkthrough that plays by itself or just have him play the entire soundtrack. He could also just cycle through random Metal Gear phrases all placed into one folder I believe. That would make it possible to make him at like he was "in character". Or maybe swap out the memory card to engage the "in character" version. Still have to play with the options.
Lots of options for "mkI" using just a digital photo frame for his brain.
As far as being able to play Snatcher on him, honestly I have no background in PC building so I hope to eventually find a capable person to help after I've completed the "MkI" version of MkII.

A fully functional PC inside Metal Gear open up kinds of weird possibilities. I could play an MSX Solid Snake game on him or go wifi with him and post on JunkerHQ forum! However hooking up a mouse and keyboard to a robot seems kinda dorky. He ends up just becoming a funky case mod.
I'd really like to get the head to move a little bit too but again I have no real life experience with servos and micro controllers for that kind of thing. Lots of tutorials online though for homemade animatronics.
Here's where I'm at with the blueprints-
Nick