TS Login defaults

We have some users who are connecting to our terminal server who have
a default login name which is filled in when they attempt to log in.
This name is not set up in the connection properties, and does not
seem to correspond with their windows login name (all machines are
Win98). It is also not the user name of the last person who logged in
on the terminal server. Is there a registry setting on the client
machine that sets this login name default?

TIA,

Jessica