Yeah PS2 emulation is very CPU intensive. I got it running somewhat decent depending on the game on a 3.2 GHz AMD CPU but when I upgraded to a 4 GHz AMD it ran much better for me.
NullDC is going to be hit and miss on a game to game basis.
Yeah, Dolphin will be a no go but give PPSSPP a try. I was able to get some playable stuff going on my 1.5 GHz laptop, but it too was a game to game basis deal.
I just inherited an older 2 GHz AMD system from my parents I need to get that thing setup and do some testing on it.