Performance of child processes

I have an application whose performance depends on how I
start it. If I start it from a cmd window, then it runs
great, but if I start it from a shell in my editor (which
uses a cmd to execute commands) then it runs about 3x
slower. In either case, the Task Manager says that the
process has the same Normal priority. I never had this
problem in Win2000 (or 95 or 98, even).

When I do a Performance monitor on the process, it spends
more time doing I/O writes (the application displays
graphics and plays sounds, so I guess these writes are to
these devices).

Any ideas why the application runs faster when launched
from a cmd window as opposed from a cmd that was started
by another application?

Thanks in advance,
Brian