The conversion between Mac and PC is fairly simple really. Most of the wierdness stems from the diference in the way the two OS's handle extra information about files. Macs embed things like icons into a resource fork, which is something PC's do not have. Thus the .rsr was born, as a holding place for the preview icon on PC's. Why in the first place they didnt just use a little jpg or png like they do in propack is beyond me. Anyhow, if you view a cr2, etc with an rsr on a mac you will see the shruggin guy icon, and if your mac version is viewed on a PC without having first created an rsr you get the same issue. That is the primary problem when moving files cross platform. The file will still work but you get no preview icons. As someone above mentioned there is sometimes a problem with the / or : in a file path, but again, once you know the issue it is easy to fix. In the end, data is data regardles of what platform it is on. P4 just didnt get built to be comeplety cross platform in these little areas' Hopefully P5 will address these issues. So, if you are using a Mac get the Macconverter program. That and a zip file maker are all you need. If you are on a PC, Stenosofts P3DO explorer has some great and easy tools for converting rsr to png and back again, etc. And there are some other tools that will work as well.