To access your SD card all you have to do is plug your Droid X into a computer. Make sure you mount the SD card by pulling down the notification shade and selecting the USB Connection panel.
Now if you go to "My Computer" you will see a removable drive appear, that will be your SD card.
You can also just remove it by taking the battery cover off and pulling it out then putting it into a computer.
To make songs a ringtone go into your music player, find the song, long press on it and choose to make it a ringtone.
You can also access it via a file explorer you can download from the market. But the easiest way to put thing on and take things off is to plug it into a computer.
