Security Rights

Hi, I was wondering if anyone can help. I have a folder
for which I
want to give certain users full control except the delete
right. I
have setup 2 groups, one to give full control and the
other to deny
delete and added the users to each group. This kind of
works, users
can make changes to files and save the changes. They can
save files as
new ones however they recieve and error message stating
that the file
already exists and do you want to overwrite it (obviously
the file
doesn't exist). If the user choose yes then the file is
saved and they
can then make changes to it. If they choose no the file is
still
created, but it's empty, on both occasions a tmp file is
created.

Any help would be much appreciated.