I had this same problem and it drove be crazy for days. I started digging around the official blackberry site and discovered a blurb about compliant file formats for ringtones.
The 8800 will not play wav's as ringtones. It will play mp3's however.
I converted my wav's to mp3's with conversion software i downloaded at River Past Software - Audio and video recording, conversion and editing
The trial software will only convert files less than 2 minutes in length.
I'm sure there are other converters out there without this limitation.