The Gamemaker skins are all fairly neatly laid out, so it would be possible to copy and paste the skins, as long as you can:
a) - Get the SIMS skin into an art package.
b) - Get the gamemaker .DDS texture into an art package.
.DDS Textures are compress DirectX textures, and can easily be converted - you can even use DB to convert them because DB has .DDS support so you can load .DDS into DB as an image then save it out as a bitmap for editing. After saving your new texture, your best to use a hex editor to change the .X file to look at your own texture instead of the old .DDS one.
Van-B

The nature of Monkey was irrepressible!.