As dtsig said, the supplied USB cable will connect your Droid X to your PC and allow you to move the file to your PC in a matter of minutes. Forgive me if these instructions are written as if you have no idea what you are doing...i would rather do it step by step and you already know it, than to assume you know some of it and actually dont...it is not be trying to "dumb it down", but only to make it simple.
1) Connect the USB cable to the phone and PC...wait a few seconds...
2) That few seconds was to allow the SD card to "mount" if it needed to in order to be read by the PC. If it didnt "mount", then it more than likely is in "USB Charge Only Mode"..and we will address that next.
3) Now, reach up and "drag" down the Notification Bar Screen...anywhere in the middle of the bar will do and just "tap/drag" at the same time should work.
4) If it opened properly, you should now see "USB Connected"...tap it to bring up a pop-up window with 4 options. USB Mass Storage Mode, USB PC Mode, USB Charge Only Mode and Windows Media Sync Mode...we will be using USB Mass Storage mode, so tap it..
5) You may see in the Notification Bar an icon of an SD card doing a little "dance"..this is the SD card mounting again...its normal. Once it does it thing to completion, your PC is likely to open a folder showing more folders...this is the contents of your SD card. If it doesnt, we can do that manually by gling to My Computer and click the "new" drive that has popped up...it should read as 16GB or so...
6) If this is a video you took with the Droid X video camera, we will need to navigate to the DCIM folder of the SD card. Once there, just find the video file you are looking for, and "right-click" it, and then go to your desktop on your PC and "right-click" again and select "Paste". Done.
7) You can now open a new e-mail and attach the video file and send it away...
BTW, the most common reason for videos not being able to be sent on a Droid X is the video mode is set by default at the 720P HD setting...which means a 5 minute video can be upwards of 100-300MB in size...MMS messages can not take files that large. If you want to shoot video and be able to message it to others, you need to set the video mode to QVGA or the like in the video camera settings...
Hope this helps...