Before attempting anything more complex, the first port of call is lowering the game's graphical demands. The most impactful settings are often the biggest memory hogs.
Cossacks 3 is a 32-bit application, meaning it is traditionally limited to using 2GB of RAM. The "Out of Memory" error often triggers when the game hits this ceiling. Use a utility like "Large Address Aware" (LAA). cossacks+3+out+of+memory+work
The "Out of Memory" error for this game usually falls into one of two categories: Before attempting anything more complex, the first port