is there a place on itunes that has ringtones for the 3gs? secondly are they free? if not on itunes how does everyone get the ringtones they would like?
either:
buy ringtones from the apple store (they arent free)
jailbreak and search cydia (can be tricky if you don't know what you are doing)
download a ringtone software maker such either from the app store (though they don't always work) or from the web such as this one.
download iringer on pc then choose a song from your music libary it will allow you upto 40sec of track time from any part of the track. it copys thevversion straight to your itunnes ringtone section then all you need to do is sync!!!