With a lower end system, you definitely want to knock down the
bdg.txt entry "LANDSCAPE_TEXTURE_SIZE = 2048" to "= 1024"
This will keep the performance closer to what you are getting
with the unpatched program. Note that the original cd is from
2005 (v2.01); a current cd from A2A is I think v2.06, the last
official A2A sponsored patch level, and from about 2007. v2.11
is from 2011, and has heavily advanced the graphics with higher
res textures and 3D ground objects. It takes quite a good machine
to run at high settings. Key settings in the Options GUI are
Particle Density - the most futureproofed entry, no machine can cope
with a setting of "Full" when ground AA opens up. Choose medium or low;
Ground Object Density - non-essential 3D objects; Horizon Distance -
cut it back if you get "stuttering" when turning with the horizon in
view, especially at higher altitudes.
More discussion here:http://www.a2asimulations.com/forum/viewtopic.php?f=17&t=10091