I know that you have to use Window's Media Player, but what if it's not finding the device? Is there anything special you have to do in order to sync Mp3's from your computer to a Samsung Reality phone??
With Windows Media Player open, connect your Reality with the USB cable, then click on "Sync" and "Refresh Devices" in the top tab. It may recognize your device this way.
If it doesn't, it may be a matter of the device drivers didn't automatically install. This happened to me with a couple different phones, and I had to go the manufacturer's site and download them from there. Sometimes you can find the drivers in the Verizon support section on this site too.