They're stored in the registry so here's the registry information for most of them, haven't beaten the game yet so I'm still missing one skin.
(Classic skins are unlocked via a pre-order code, Altair skin is unlocked via a code you get from registering the console edition but it also works on the PC version, Prototype skins are unlocked from collecting all 1001 seeds and the Jade skin is unlocked by completing the game.)Link
Sendspace link to the registry file I uploaded, it's clean and should work on most Windows OS's without problems.
(Feel free to edit it and check it out if you want.)
Reg information for this is stored in the "[HKEY_CURRENT_USER\Software\Ubisoft\Prince of Persia\1.0\Game]" location.
(Does not affect savegames or anything like that, just unlocks those skins via the ingame options menu.)