I have a document library in SPS 2007 with versioning. When I
select "Edit Document", a message pops up saying the document will be
checked out, click ok and MS Word 2003 opens with a shared workspace in
task pane that shows me that the document is part of a sharepoint site
and gives me an option to checkin. Also, if I exit Word without
savings, it gives me a message box with 4 options (Save and checkin,
check in without saving, etc). HOWEVER, this behavior does not happen
in all machines. If the same user logs in to the same sharepoint site
and opens the same document, MS Word does not open the task pane at
all. If I open this task pane manually, I do not see any reference to
Sharepoint at all.

The machines are similar, same versions of Windows XP, same versions of
MS Word but probably other software installed differently or installed
in different order.