From what I understand, there are several "formats" of DVD drives out there in circulation (DVD-R, DVD+RW, DVD-RAM) and data burned for one is not always compatible with the other.
The FP iMac uses a DVD-R, while many PCs use DVD-RAM. Perhaps incompatible players are the problem, rather than an issue with burning for "Mac" or "PC".
If it's a player issue, I'm not sure there's much you can do. If the players are the same, maybe check out Toast 5 and see if it can meet your needs.