Even with all the refinements they've done, the game still runs out of memory in big maps or long games.  And if the map is bigger the empires get bigger, and the more players in the game, etc.   If you have a safe memory defragmenter, you can Alt-Tab out of the game, defragment memory and then Alt-Tab into the game, but if any Windows windows appear over the game screen it will crash with a DX Error, so make sure you save the game first.

PS: This is on a 64-bit system that has a bit of extra leeway because of extended memory addressing or somesuch, however I only have 4GB of RAM total.  I'm not sure the maximum amount of RAM that can be addressed on a 64-bit system with the LH 1.7 code.