Conserve RAM usage?

I am pretty computer literate, but I was wondering for the rest of you out there: can I do something to compensate for a low amount of RAM on my computer? I recently purchased RollerCoaster Tycoon 3, and after a couple of days it would crash after about 10 minutes. I got the "Could not allocate memory amount" message each time. Is there some sort of trick or program that could help? Also, I'm due for a hard drive defragmentation: will that help?