Depending on resolution (e.g. 1680x1050 or lower), that PC would play a lot of games on high settings, although your CPU will be a bottleneck. If you haven't already bought these parts, spending a few $$ more for an Athlon II X3 440 would probably help a lot.
The price difference between Athlon II X2 245 Regor 2.9GHz ($59) and Athlon II X3 435 Rana 2.9GHz ($71) is really quite small @ $12.
Unless you're under a lot of pressure on your budget its a pretty good bargain.
It looks like that RPG game doesn't run quite as well on AMD CPUs as it does on Intel CPUs.
It's looking like even the X3 440 would not help you anymore than your current CPU.
You can test turning down the graphics settings and see if that helps at all.
And test with the sound turned off to see what effect that has on performance.
Empire: Total War is primarily stressing the CPU according to a benchmark check
(click the chart to get the rest of the article and it's notes)
So then, if the CPU is the problem, what's the most cost-effective fix? I agree with WR2 on playing with the graphics settings to get more data on the problem. Are any other background tasks running that might be paused or terminated? That's one area where an extra core or two can make a notable difference.
As an example, the college where one of my nieces is a student requires them to use Cisco's Clean Access Agent and other security software; another's college has inflicted McAfee upon them.
Well, if you look at the gaming CPU chart at http://www.tomshardware.com/reviews/gaming-cpu-core-i5-... you can see that a three-tier jump over what you have isn't too expensive. As WR2 points out, the particular game is rough on any CPU, so improvement in that one may be meager (but I think noticeable), but you'll probably get improvement in other games too. In any case, unless your tests in specific games show otherwise, I'd expect your CPU to bottleneck your GPU, not the other way around.