mapped drives kill network access when fileshares not available

Some of my domain clients run VPN software to allow them to connect to
another IP network occasionally. For security reasons, we have their
machines configured so that they can only connect to one network at a time,
so when they connect to this other network domain resources are no longer
available to them.

We are finding that when they are logged into the Windows domain, and then
make the connection to the other network with their VPN software, their
network connection is brutally slow until they unmap the network drives they
were connected to on the domain side. It seems that Windows keeps trying to
re-establish those mapped drive connections once they are no longer
available, and this keeps their network hardware/software very busy.

Short of writing a batch file for them to unmap drives when they want to
start their VPN session, is there any way to tell Windows to stop looking
for those network drives until the user actively attempts to access one of
them (once they've killed their VPN session and have reconnected to the
network that the domain is on)?

The clients are Windows 2000 SP4 running on a W2K3 domain.

Thanks for any thoughts,

Phil