Quoted from chooch:Building the PC is the easy part but setting everything up to have a nice front end can be overwhelming. I have a MAME machine that cost a few grand when new and it has a really nice trisync crt monitor however the front end is dated and I dread having to start all over. Setting up another front end is pain which is why the machine pretty much just sits there and collects dust.
That's why I suggested Launchbox. You can set the whole thing up in 15 minutes and have a nice arcade front end with BigBox. Anyone with access to YouTube can have a nice setup in an afternoon. Heck, I didn't even build my PC. I just bought a Dell Optiplex with a 3rd gen i7 for $95 shipped and it plays everything well without a graphics card.