Well this may explain the problems....perhaps?

hes running on low setting so 512 should be fine but for sure like i said its the cpu the gpu would be a problem if he is at max settings. but i know when my hdds are cluttered up or havent been cleaned over i start running into jerking motions on bc2 or other games. you see that the minimum gpu memory is 256 and recommended is 512 the clock speed and shader clock does matter but only if the settings are high and the ram is minimum and recommended 2 gbs so with 4 gb of ram he should be running smooth so depending on latency and clock speed of memory that shouldn't be a problem. the last thing that could be wrong but very inlikely is not enough power for gpu but more than likely he has enough with only having a 65w cpu so that leaves only hdds which he keeps clean, heat wearing down the system too fast or the cpu being a slow butt and not allowing info to be processed fast enough.

Well I guess I'll throw my two cents in. I'm going to have to agree that the CPU is your real bottleneck at this point. Problem is, an upgrade there will require an upgrade to the mobo and most likely RAM (if you get a newer mobo/CPU combo). Add in the fact your now using extra wattage for a more powerful CPU and you may also be looking at a PSU upgrade. The other bottleneck your going to run into will be the HDD. I was running 4 GB PC6400 (800MHz DDR2 RAM), an AMD Phenom X4 9850 (quad core), and an ASUS mobo (M4A78?? Can't remember). The rest of my rig was the same as what I've got in my signature. Even after my upgrade I still manage to get some rather crappy framerates on the bigger maps (I use modified Medium settings at 1920x1080) and during explosions/building collapses. My bottleneck right now is the HDD. I'm still running two 7200 RPM drives (granted the faster Black series has all my games/OS), but I probably won't be able to see any solid figures until I slap a SSD in my system. For me personally, it's not a priority right now and I probably won't do it until my next major over-haul (ETR next decade sometime LOL). Basically what I'm trying to say is, you're probably going to be looking at building a new rig rather than expanding on the one you have for any real significant increases in performance. So the question now is, do you wanna?

yeah that is what he is probably going to be doing.