Mac kits and PC kits are the same thing.
They will normally come as a compressed file (.zip or .rar format). .zip files will work on the mac without extra software. rar files need extra software installing such as stuffit expander (google it).
Once you have them decompressed you just need to put them in the right place. I don't use a mac but i'd guess there is probably a 'sports interactive/football Manager 2007' directory where user documents are kept.
Simply put your downloaded stuff (picture files AND config.xml files) in there. You could make your own directory structure in that folder too if you like to make things easier (eg kits/eng/
prem/ or faces/eng/champ/) and put your files in there.