Help with AS-Mothership

[Matthew Arnold]

What tweaks might I be able to use to get AS-Mothership to be playable 
on my system? I've got an Athlon XP 1800+ with 512M PC2100 and an NVIDIA 
GeForceFX 5700 Ultra using the 1.0-5336 drivers. When I go on to that 
map all by myself in Instant Action with my normal settings (1024x768, 
everything at "Normal") I can barely keep 20fps. It is utterly 
unplayable in single player with bots. Even if I lower all the settings 
to "low" or "lowest" wherever applicable at 640x480, my framerate will 
average around 9 fps with bots.

I tried to fight through it and let my bots do the work so I could at 
least complete the single player assault. I made it through my attack 
relatively decently and was about 80% of the way through defending when 
I got an (in)famous karma crash. I wasn't a happy camper.

Yes, I know that a faster CPU would help, but this is the only map I've 
found (and I've played through all of the other assault ones) that is 
utterly unplayable on my system.

Any thoughts?
   Matt