You sure you are using an MMC card? Sometimes folks get an SD card and try and put it into these phones. The cards are very similar in size. The SD cards are a little thicker than the MMC, other than that they look the same.
I have a nokia 6255i, which is very similar to your model. I was able to install a 1gig MMC card and fill it with music with no troubles. Once you have the music on the phone, go to GALLERY, find the song you want to use, choose OPTIONS while the song is highlighted and then pick SET AS RINGTONE.