If those cards work with Book I, then they should work with Book II. Book II has a much more optimized engine and although the game is significantly more detailed, it actually uses less system resources to run.
Well, I coul play E1 with a ATI rage 6 AGP 32 Mo !
That's because I only have an old G4 450 dual, and I don't have any money to buy a new one, as many people.
Actually, I hope E2 will work with the same card too.
Except in the cities where it could be quite slow, but working anyway as I was expecting with my computer, it was nice with all other parts of the Eschalon universe.
So, I guess you'll haven't any problem with 128Mo...