A free patch is now available to allow EndNote X1 to work with Word 2008 on the Macintosh. See:
http://www.endnote.com/support/CWYW_Word_2008.asp

Note the following posting from the EndNote discussion forum:

If after installing the Word 2008 SP1 update and the EndNote X1 2008 update the tools still do not appear:

1) Close Word and EndNote

2) Open your hard drive and go to Applications:EndNote X1:Cite While You Write

3) Copy the files “EndNote CWYW Command.dot” and “EndNote Web CWYW Command.dot” by highlighting them and going to “Edit > Copy”

4) Go to the folder Users:[your login name with the house icon]:Library:Application Support:EndNote and paste the two files, “Edit > Paste”

5) Go back to the folder Applications:EndNote X1:Cite While You Write

6) Copy the file “EndNote CWYW Word 2008.bundle” by highlighting the file and going to “Edit > Copy”

7) Go to the folder Applications:Microsoft Office 2008:Office:Startup and paste the file, “Edit Paste”

8) Start Word, go to “Word > Preferences” and click on “File Locations”

9) If the Startup folder is not set, highlight “Startup” and click on “Modify”. Select the folder Applications:Microsoft Office 2008:Office:Startup and click “Choose”

10) Click “OK” and close Word

11) Start EndNote and then start Word

The Library provides Endnote support to all staff and students at the University of Queensland regardless of which operating system or platform you run the software on.

The Endnote section of the Library web site includes links to a variety of support resources for both PC and Macintosh users including installation guides, troubleshooting tips, filters, connection files and links to resources available from third party sites such as the University of Maastricht and the Thomson site itself.

That section also links to an online discussion group where questions can be posted to other Endnote users and links to both Ask IT (for students) and Ask A Librarian (for staff) for additional assistance.