Windows XP / Server 2003 Remote assistance

Hi,

I have a question about the remote assistance with xp / 2003. When I request
assistance with my windows XP client I can use 2 different methods do send
the invitation (Messenger or Outlook Express / Microsoft Outlook). When I
request assistance with my windows 2003 server I have also 2 possibilities
to send the invitation (Messenger or generate a mail with a link that points
to Microsoft). On XP and on the server OS Microsoft Outlook is installed.
Why can't I use directly Microsoft Outlook to send the invitation like I do
it with XP?