To the first two halftards who can't read.
The OP is asking if he can make one of his iTunes tracks to show as a ringtone on his iPhone.
Sjeez it's really hard to read apparently for some.
Yes you can make a ringtone out of 1 of your favourite tracks but, it has to be around 30 seconds long.
You can edit it the track in audicity or any other editing programs and then save it as .m4r. you can then put it in the ringtone part of your iTunes library and sync it to your iPhone.