Denys said:

Bottom line, the answer to the original question is: no, you cannot
connect a
dumb terminal to an existing 10BASE-T network.  You must connect it to
a medium
access device, such as a DTC.

While this is correct, you can still use the existing 10BaseT cabling
to connect the terminal to the DTC.  This way the terminals aren't
interfering with the network and you don't have to run separate cable
for them.  Upgrading, should it be necessary, is simple.  Just replace
the terminal with a networkable pc and move the patch cable from the
DTC to a hub.

Bryan