how do i download themes onto my htc touch ?

i want to try to download different themes for my phone (like make the screen look like an iphone) but i down no how to do it. I dont want to do it by going to the internet on my phone, i want to use a usb cord to hook it up to the computer, so if you could put down a website link to where i can download one for free virus free that would be great:D thanks-