You'll need a USB-to-cell phone cable, commonly called a "tether." Normally tethers are
used to provide internet connectivity via cell phone to the computer (sounds desperate
and terribly slow, but not only is it possible, its better then nothing). Its also useful for
uploading pictures from camera phones to a PC/cloud.
The tether for your phone will have a USB type A port on one end (for the computer)
and a connector on the other end (for the cell phone) that's called a USB "Mini-B" connector (since you phone has a USB Mini-B port).
This cable is very commonly available, since its used for digital cameras (and nice MOTORAZRs).
Here's a link to one manufacturer's "USB Data Cable" for your phone:
http://www.wirelessgalaxy.com/motorola-rival-a455-oem-micro-usb-data-cable.htmlI'm not endorsing www.wirelessgalaxy.com, its just that they have a nice photo of your tether.