Windows implements the rasterization of truetype fonts differently to the Macintosh, therefore if you have EXACTLY the same font on both platforms, windows is going to be SMALLER, or BIGGER, or rarely THE SAME, but it's not consistent, you have to check it and check it regularly.Together with Director's lousy text handling in general this is a major incentive for going with pre-rasterized bitmaps of text wherever possible, but frequently this isn't feasible. Otherwise, do all final text layouts on the their target platforms, and as ever "test early and test often".
Other tripwires:
Quicktime can only be played directToStage in Windows [see section 8]
Director for Mac doesn't (can't?) support AVI-format digital video.
Sound playback differs between platforms. Particularly, sounds on the PC may play with noticeable delays on the PC compared to the Mac. There's a note about this in the DfW Read Me somewhere.
DfW seems to be somewhat more stringent about sloppy Lingo constructs such as arithmetic operations between incompatible types or voids. (I can't at present provide a concrete example of this, since it's some months since I was shown the effect and I don't currently have a Windows machine to try it out on, but my recollection is that an operation like
set x = y + zwhere y = 1 and z is uninitialized (void) caused problems. This may also have been with a pre-4.0.4 version, so I may be needlessly scaremongering, but it's always worth being careful about such things!)
2 pixel dropout on bitmapped images (?)