Modifing Across Networks In Vista

I've added my Vista machine to the networks at both home and work.
I've made certain that the Vista machine has Admin permissions.
I've noticed that while I can create new files and folders across the
networks, I cannot modify them: delete, rename, update (save as in Office
2007).
What I've had to do is save (modify/update) locally to a local hard drive
then drag and drop the modified files/folders to the networked drive.

Gateway Tech support initially told me this was an Office 2007 issue but
I've since realized that no matter what application I'm using, I cannot save
a file across the network that I've opened from network hard drives, nor can
I save to network hard drives, files that I've opened from a local drive. I
cannot modify, rename, delete, etc files I've accessed across those networks,
from the Vista machine.
I am able to modify files on the Vista machine from XP machines on the
network, just not the other way around.

Anybody know the fix?
Is there a new option in Vista that I've missed that is prohibiting me from
full access out?