Breathless on my 1.4ghz Mac Mini with 1GB ram, set to:
Window size: 192x120
Pixel size: 2x2
Is playable. Anything with more pixels and that same window size and it gets too slow.
E-UAE on my little HP DM3-1140 laptop runs it at 320x200, 1x1 pixels just fine. Not really too entertaining of a game.