Remote assistance

Question...Two Win/XP Pro boxes on the same subnet, both
logged on with users who have access to both the Internet
and an Exchange server. One is trying to use the Remote
Assistance, send an invitation (If passwords are used,
the second user can never connect...) If passwords are
not used, the second user will get the email and when he
tries to connect, the first user never gets a
notification asking him if it is OK to connect...
Please help...