>Why would a long time used app work fine on Windows 98 but cause sudden reboots on some new computers loaded with Windows 2000?

You'll have to provide more info about the problem to get any help.
What's VFP version/Service pack?
Are runtimes of the same version/Service pack as a development?
What part of application causes the prioblem (printing, previewing report, entering or saving data, e.t.c)?
Any other info that can help indentify the problem?