You can't use 6 to open a 7 file. You would have to open it in 7 and export it as 6.
Try Crashhelp@quark.com. They salvaged a file I'd created in Quark 7 beta and saved it as Quark6 for me.
Send me the file, and I can export to 6 for you if you wish.
10 meg limit on e-mail, though. If it is larger than 10 megs, ftp to me if you can.
geo@pkamar.com
You can buy Markztools for Quark 6.5 for $200 and "convert" the v7 files. They will open in 6.5. I bought this software specifically to recover a corrupt document and discovered this accidentally.