I install the latest Nvidia driver (www.nvidia.com) before DirectX and never have such an issue.
I've played Tachyon since 2000 off a demo from delta force and loved it so much I bought the game. I play it through about 4 times a year from both the Bora and Galspan perspectives. Now for some reason while playing half of the orien ship is missing and objects keep disappearing and reappearing . Wierd. I never had this problem before. I've uninstalled and reinstalled the game twice-still no help. The only thing different is I updated the driver on my gforce2 video card to 9.0c. I run dxdiag and on the test display screens 7.0 and 8.0 direct x version is full screen and good but when it tests 9.0 version the spinning cube shows up in a smaller screen and around the bottom and right hand sides the screen is flickering and jumpy. Help. Can the driver do that?