Here is some popular file conversion software:

Q2ID – Macintosh and Windows
Helps Adobe InDesign users to convert QuarkXpress to InDesign into a new file. With only one click, users can open QuarkXpress files then convert to InDesign files including images, text and fonts.

ID2Q – Macintosh and Windows
Convert InDesign to Quark into new files easily and quickly. With only one click, users can open InDesign files then convert to QuarkXpress files and ready to user or edit.

PUB2ID – Macintosh and Windows
Converts Publisher to InDesing files. A great plugin which supports Adobe CS3 & CS4 to migrate all Publisher files into new InDesign files with only one click using Indesign File -> Open menu.

MarkzTools 8 (New) – Macintosh
A great Xtensions to recover bad Quark files. It amazingly can be used to prevent and fix corrupted Quark files.

All these publishing file conversion software are available at local reseller in your country or you can find at Markzware as well.