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.
Good luck!