Editing a file on a webserver with XL2007

[LeonIloilo]

I want to edit a XL file that is on a webserver.

Using XL2003 this is no problem:
the file opens read & write.

Using XL2007 the file opens read only.
I can't even use Save As.
It says the CopyOf already exists,
and i know this is not the case.

OS = Vista Business.

In the options of XL2007, i can't add the webserver to trusted places.

What should i do,
to open a file on a webserver with XL2007 read write?

Thank you.