According to Brian Harry, TFS 2005 does not support to have Sharepoint on another machine than TFS. In an effort to address one of the most common of these requests - using a separate or pre-existing SharePoint web server/farm, we have produced a technical article that describes how this can be done manually. 2 articles on this point :
http://msdn2.microsoft.com/en-us/teamsystem/aa718901.aspx
http://blogs.msdn.com/sudhir/archive/2007/06/25/sharing-your-corporate-sharepoint-server-with-multiple-tfs-servers.aspx

In Team Final TFS 2008 Feature List (coming before the end of november), you can officialy use Sharepoint on any server and any port