The graphics card is pretty old. There is probably not much we can do.
I assume you are on low graphics settings already. There are not much more options. You could try to quickly set the clouds to 'none' to switch them off as well (upper right corner in main menu), but it might not help much.
You could also try to reduce the window size and hence resolution.
But it could be also another issue though due to card being fairly old. You might have to get a little newer card to play it.