AH3 will be much more GPU dependent than AH2.
If the current game runs smoothly with that computer, the processor will likely be powerful enough for AH3 although it's a little on the lower end.
The integrated HD 4200 will be the main issue. You would need a "real" video card with at least 1 GB of dedicated RAM.
Notice that an additional video card requires more power, so you'd probably have to get a new power supply, too.