If you haven't a tool the show the precise framerate (don't know if it's possible ingame somehow
) install Fraps to see how fast your game runs.
Anyway, lower your resolution down to 640*480 just to see if TM2 runs better. If it does, your graphic card is at fault. If the framerate doesn't improve, it is most likely your CPU that is to slow. Even if you don't want to replace the hardware, it is important to know what component is the weakest to determine what settings should improve the framerate. Changing the resolution impacts only the graphic card at most games.
Even though you might be above what the developer claims to be the minimal needed specs, your PC is really weak for 2013 gaming. Although it would be advisable to replace it (or most parts of it), if you are on a budget (and who isn't), you might just need to swap in a new graphic card for a couple of bucks to play Valley fine.
EDIT:
BTW, is your Athlon a single core CPU? If so, it is really old and per GHZ not really compareable to modern CPUs. Every core in a modern AMD chip or for example a i5/i7 should be two to four times faster than your ship. So your notebook could be easily allot faster then your PC if it uses newer parts (and therefor a more efficient architecture). The Geforce 9200 is definitely a rather slow card (was slow when it was new too).
