If you're not using a 64 bit version of Windows with at least 4gb of ram, you're going to experiences some memory issues from time to time. You can solve that by aggressively reducing the system resources consumed by the game, and restarting frequently.
Here are some draw distance settings you can put in the autoexec.cfg file. These are what I use on a higher end computer that I run near maximum settings on, you'll want to drop them down to whatever's still playable for you. Dropping them to half is probably a good starting point, possibly less than half on the xy as I pushed that one up from the default maximum.
e_detail_materials_view_dist_xy = 4096
e_detail_materials_view_dist_z = 1024
e_view_dist_ratio_detail = 75
e_view_dist_ratio_vegetation = 100