Hi Arthur,
To be more specific, keep everything close to the
original resolutions. You can easily register
EPI <-> anat <-> template while staying close to
the original resolution(s).
The template does not need to be down-sampled.
The EPI does not need to be up-sampled.
As Daniel suggested, consider using our higher
level processing programs to do much of the work.
They deal with those small issues, and you can
easily look at the scripts to understand how.
It is hard to suggest too much more without knowing
more about your circumstances and methods.
- rick