mapped drives after using RIS

On our 2003 domain, XP boxes that are installed manually never have their
mapped drives become disconnected. On a new batch I am rolling out via RIS,
all mapped drives disconnect after 45-60 minutes. This doesn't seem to be
related to the server timeout because manual installs don't do this. It may
have nothing to do with RIS (that's just the one difference). Is there a way
to tell XP to ignore the disconnect that the server performs after
inactivity? Thanks for the info.