Using AT on XP to run python script

[Chris Stromberger]

I'm having trouble getting AT on XP to run a python script for me.
Have tried:

at xx:xx "c:\python21\python.exe c:\scripts\script.py"
at xx:xx "start c:\scripts\script.py"
at xx:xx "c:\scripts\script.py"

and get "the system cannot find the file specified" for the first two.
The last version does nothing apparently--no error indication or
anything.

I imagine it is related to user accounts and such.  Anyone have any
pointers?