PSD files are not platform specific.
The PSD files are inside of RAR archive files, sort of like ZIP or SIT files. To UnRAR a RAR file on Mac OS X, simply use UnRarX free software from
http://www.unrarx.com
Ironically, the UnRarX installer comes inside of a ZIP file. Funny! Most of us use RAR because we're really not that fond of ZIP fles.