I produce artwork in ID CS2 on Windows at work and these occasionally need to be passed on to the other designers who all use Macs - we've never had a problem doing this. If the document is created on a Mac in the first instance, give the filename a .indd suffix - that way, Windows will identify it as an InDesign file.
The only area where you might come unstuck is with fonts - it doesn't necessarily follow that the Mac and PC versions of a particular font:
a) have the same name on either platform, meaning you might need to do a Find Font and replace
b) that characters in a font will have the same widths on each platform, which means that you may get different line breaks on paragraphs on the Mac to what you'll get on the PC