My previous Motorola Razr v3xx allowed quality bitrate and 14-15 seconds in length [FOR ringtone], however this varies with type of phone. Less, likely, for cheaper, old phones/models, and equivalent, or higher in terms of bitrate, for more expensive phones.
Be sure to get at most 10 seconds of a tune for tests, and save into a format your phone supports. Likely MP3. The edits are really simple; Goldwave works, Audition, CoolEdit Pro, Sony Vegas ...
Be sure to go for a standard bitrate to begin with, and work from there, as saving in anything higher may just be rejected by your phone at the applying as ringtone.
Oh, and also. What phone do you have [model]? Depending on the brand and model, you're either able to settle for convenience with a simple insertion of a MiniSD[Readers come to good use: I use this; supports all sizes of SD, so long as you purchase the one with the MiniSD port], or a boatload of problems going PC via USB. As Motorola, for certain models, only allows data transfer through software purchases, such as their PhoneTools, and depending on your operating system, you may have more than a few roadblocks to get around. Personally, this is an issue I only faced with the Razr models, as they do not support MiniSD cards.
Either way, once gotten used to, I find this far faster and far more convenient than doing anything remotely.