You didn't mention whether you're using PageMaker on a Mac or a PC. If I'm not mistaken, Quark is available only for the Mac, right?
Maybe you'll find something of help on this page: How to transfer Quark Xpress files between Macintosh and PC
There's also a reference at the very bottom of this page to PageMaker 7 for Windows
According to this page on the Adobe site, there's apparently a PageMaker 7.0 Converter for QuarkXPress
, but it refers to Quark 4. Maybe it can be updated or already works with Quark 7.
Essentially, these links are merely the result of a Google search, and I've barely skimmed the contents of the pages. Very possibly they'll give you some ideas for further searching.