Cross forest/domain drive mapping

A company is divesting from it's parent. As a transition
step, we want to establish a bridge across the networks
then start to transition applications that only use
servers located at the "child" company. However, these
servers will still be a part of the parent forest and
domain (win2k) at the start of the transition. The
applications use win98 and must map with permanent
connections to drives on the app. server on the parent
domain. Can someone help us understand how to set up the
dns or other mechanism for this transition step. We can
get logged on to the "child" domain, but are unable to map
to the drives. We also cannot ping the dns name of the
app server. Do we need to establish trusts between the two
forests/domains?

Thanks Very Much for all help and guidance.

Diane