I've posted this guide that I pieced together from several places a few times. It is an absolute step by step guide at how to create ringtones from any song in your itunes library. I can't remember exactly where I got it, and would attribute it if I could remember. Feel free to PM me if you are unable to get it to work, I, like many others have created and synced ringtones on both mac computers and PCs so could probably help you if the guide doesn't.
For PCs
1. Start iTunes and find the song you want to convert into a ringtone. (It must be an MP3.
2. Right-click the song and choose "Get Info."
3. Click the "Options" tab.
4. Check the "Start Time" and "Stop Time" boxes, then enter times for each (no more than 30 seconds apart, the maximum length for a ringtone.)
5. Click OK, then right click the song again and choose "Create AAC Version." You should immediately see a new 30-second version of the song.
6. Drag that version out of iTunes and into the folder of your choice.
7. Delete the 30-second version from iTunes and undo the start/stop time changes to the original.
8. Open the folder containing the 30-second AAC file that you dragged out of iTunes, then change the file extension from ".m4a" to ".m4r." Double-Click it and it immediately gets added to the iTunes' Ringtone library.
How to turn file extension changing on
(Do this either before doing anything, after creating a folder with your ringtones, or at least before step 6 in the above sequence.)
1. find the folder that you dragged the file into from step 6 above.
2. click the dropdown box that says "organize"
3. Click the option that says "folder options"
4. click on the tab that says "view"
5. un-select the option that says "hide extensions for known file types."
For Macs
How to create custom ringtones for iPhone 3G using iTunes for free?
The following steps show how to create free ringtones for your iPhone using only iTunes and songs you already have on your computer.
Note 1: This method only works with songs that are DRM free. To make iPhone ringtones using DRM protected songs please follow This Guide to remove the DRM protection first.
Note 2: If you want to avoid the trouble of making custom iPhone ringtones by following the steps below, you can simply get an iPhone Ringtone Maker Tool to help you easily and quickly create ringtones for your iPhone.
To make iPhone ringtones using only iTunes:
1. Right click on the song you are going to make into a ringer and select "Get Info".
2. Go to the "Options" tab and go down to the "Start Time" and "Stop Time" check boxes. Check both boxes and input the time you want your ringer to start/stop. The ringer has to be 30 seconds or less. Click "OK" when you're done.
3. Right click on your newly "clipped" song and select "Convert Selection to AAC". The song will be re-encoded using the start and stop times determined (If your menu item does not read "Convert Selection to AAC" and reads "Convert Slection to MP3" (or some other format) please go to iTunes -> Preferences -> Advanced -> Importing and change the "Import Using" drop down menu to "AAC Encoder").
make free ringtones for iPhone, create free iPhone ringtones
4. After the song is done encoding navigate to your iTunes Music folder, locate your song, and drag it to your desktop. After the song is on your desktop go back to iTunes and delete the clipped version from you iTunes library (It won't delete it from your desktop, it will only remove it from iTunes).
5. Go back the song on your desktop and right click on your song and chose "Properties". Go to the name and extension section and change the extension from .m4a to .m4r (or you can just change the extension right from your desktop).
6. After the extension is changed simply double click on the file to add it to your iTunes library under the ringtones section. Sync your phone with iTunes and you're done!
Note: Remember to go back into iTunes and uncheck your custom start and stop times for the original version of your song.