Many users have tried that hack and there hasn't been very successful stories yet. Even if you get it to work, the phone will delay to play your ringtone since it's on your memory card. Please refer to this thread since it has a different hack than the one you did and it can help you clear things up.
http://ppcgeeks.com/wm5-registry-hac...+location.html
Also, if you are using mp3s as ringtones, what I do is use an mp3 editing software to extract about 35 secs of each song and lower the quality a bit, then just transfer that file to the phone. That way:
A. It plays the portion of the song I want.
B. It saves space.
C. You don't have to mess with your registry.
D. You get the same results you would if you had the complete file.
Hope this helped.