I use sony soundforge to make all my mp3 ringtones.
I save the finished tones with these specifications...
56KBS
22050Mhz
Mono (channels)
To transfer them over to your phone ... you can use
MP3RINGTONES4U ... that is through using the internet. you upload a song through that site, you receive a text message and follow the link in the message to download the tone to your phone. No extra charges or anything. I know because I use it to send tones to family and friends.
OOR, you can invest in a data cable for your phone or a bluetooth usb adapter. Only difference between the two is wired vs wireless. Once you have either of those, you can search around for the Motorola Mobile Phone Tools to sync your phone with your computer. You can then transfer files between your computer and phone.