Google was not very friendly, and neither was the eMachines site; I could not find actual specs. A rear-view shot though showed the PSU has a little voltage switch. That probably means it is a very marginal unit (e.g. a Bestec). The strongest card you could even consider is a HD7750.
Edit: If all it has is AGP, then I agree with namdlo; any money spent on it is wasted.