MC10 cannot do this currently, because it's automation options don't support folder "searching". You can import files from the command line, but only by specifying each particular file. In MC11 you can do this by setting up an entry in Windows' Task Scheduler that runs:
c:\windows\system32\mc11.exe /SilentImport [path_to_files]
In this way, you can set MC to update as often as you'd like by using the Windows Task Scheduler capabilities. MC does NOT have to be running for this method to work, though you do have to be logged into Windows (I believe).
If you are feeling particularly lazy, and don't feel like using the Windows Task Scheduler, you can also use KingSparta's great auto-import plugin which can be found
on his web site. It works essentially exactly the same, except that MC may have to be running at the time for his method (I'm not sure, King?).
Both of these options are version 11 only though.