Assigning mp3s as ringtones?

[AbsolutZero]

I have a Katana DLX and my service provider is sprint. I have downloaded bluetooth songs from my computer and put them on the phone but I can't figure out how to assign them as ringtones. I've been goofing around for almost a week now and can't figure it out.

There is a website I used to use that worked perfectly but when my hard drive had to be reformatted I lost the bookmark for it. If anyone knows any sites that are 100% compatable with everything please let me know.

Thank you!