Read her excellent article here. Here's a brief recap...
General File Conversion
She specifically recommends two universal translator programs, MacLinkPlus Deluxe (for Mac) and its Windows equivalent, Conversions Plus, both from Dataviz.
Converting Layout Files
For those feeling the pain of converting layout-intensive files, she recommends Markzware plugins, which can convert Quark files to InDesign and vice versa, AND can do it cross-platform.
Fonts
Her Geekness also mentions a Mac/Windows font conversion tool, TransType Pro, from FontLab (for both platforms), which eliminates headaches caused by Type 1 fonts that are specific to one platform. I'm looking into this one especially, since I work in a mixed environment of Macs and Windows machines, and the font issues can be vexing.
Microsoft Office 2007-08 Files
And she tackles the new Office formats (.docx and the like). She says:
If you’re on a Macintosh, there are many free and low-cost utilities that convert the “x files” to earlier versions of Office programs. The official Microsoft converter is still in beta and is called the Open XML File Format Converter.. My luck with it has been hit-or-miss, though; and ditto with many of the freeware converters you’ll find if you Google “convert docx.”She also points out that "If you use Leopard (Mac OS 10.5), you have good access to Microsoft's new format even if you don’t own any version of Office. TextEdit 1.5 can open .docx files, maintaining even the most complex formatting, and even save files in .docx format!" (my emphasis)
