Sure, here's how you can get the skins to work.
First, extract the "Out" folder from Loop's Spidey skin .rar to your desktop or wherever.
Then, open up TexMod and click the folder button on the top left hand side that says Target Application. Find the Game.exe file in C:\Program Files\Activision\Spider-Man 3 then select it and click open.
Now, click the small folder icon (above the X) and navigate to the "Out" folder you extracted from the .rar then open the h.tpf file. It should show up under Package Names now.
Click on Run and the game will load with the new skins.