Ah...I see. Personally I prefer the "do it yourself" method, as it gives you more control. For wallpapers, just take a nice pic, crop what you want, and then resize it to fit your phone's screen (you can do this with photoshop or with the phone suite on your computer). Once you got that done, just use the USB data cable or bluetooth connection to transfer the image to your phone.
As for ringtones, if the phone can handle mp3's you can use programs like Adobe Audition or Audacity to crop a section of a Kamen Rider theme song or soundtrack song (e.g. take a 4 min song and crop it to just the 20 second chorus) so that you won't use up ALL of your phone's memory. Then, as with the pics, just use the bluetooth connection or USB cable to transfer them from your computer to your phone.
If you're looking for KR ringtones in MIDI format, sorry bud, I personally can't help you there.