I decided to try and start the game again even though I had not changed anything on my system since my above post. To my surprise it worked. I have started in a couple of times now with no repeat of the original error. Don't know why...didn't change a thing.
Frame rate is around 30-40, except when firing at the ground or another plane at which time it drops to 17-20.
I am running Win98, AMD XP1700, Nvidia Geforce3 Ti200 (latest Nvidia reference drivers), and DirectX 9 (off the windows update).