Last time it was asked for, the team had no interest in releasing the source. Some quotes from #mta from Monday, February 22, 2010:
As per my signature, I've updated MTA 0.5's SCMs as best I could, but as of yet all that effort has amounted to nothing due to lack of developer support. Perhaps it's my fault for wasting time on it in the first place.
Sorry, but unfortunately the answer is no at this time.
can mta/gta use more than one core? i dont think so..
It's still beneficial for the rest of the system as background processes can use other core(s), leaving GTA/MTA to use most of one core for itself.
Pedestrians and traffic vehicles in single player are generated from specific nodes, and appear only when you're looking. If you turn around, they disappear. Here's a lengthy thread about this topic.
Your graphics card is integrated and is very underpowered. You can try updating your video driver, but it most likely won't help. If you tell me your motherboard model then I can find the latest driver for you.