Document not saved

I have see quite a bit of talk on forums about this issue, but I have never
seen a fix for it or even a definitive answer of why it happens.
I am running Vista Ultimate and Office 2007 on a brand new computer. We
have several files which are on a Windows 2000 Server which I need to open,
modify, and then save back to the server. The problem is that I can open the
file, and modify the file, but when I attempt to save the file back to the
server I get the error message: "Document not saved". This happens in both
Excel and Word. I also have Office 2003 on the same computer and when I open
either types of files in Office 2003, I can open, modify and then save the
files back to the server with no problem.
I have full rights to the directory/files on the server.
This indicates to me that the problem is not related to Vista, but rather to
Office 2007. (or maybe it's a combination of the two?)
Thanks for any help on this....I am holding up purchasing more computers
with Office 2007 until I get this issue straightened out.

Does anyone out there know of a fix for this????