I downloaded a tar-ball into my Documents folder. However for the life of me I cannot find it when I use the terminal window. I used the "find" command and came up blank.

/home/user/MyDocs/.documents

It's a hidden folder.

It's actually "/home//user/MyDocs/.documents". For some reason I can't fathom, Nokia chose to hide the directory.

Never mind... I found it. I do have another question though. When I connect through the USB how to I navigate to MyDocs? All I see is maps and a couple of videos my N810 doesn't seem to see.

When you connect through usb you can only see the internal memory card (/media/mmc2) and the external memory card if you have one installed (/media/mmc1); you cannot access the other folders on such as /home/user: they are in separate memory which isn't accessible via the PC. In addition, while you are connected from the PC the N810 won't be able to access those memory cards.
That is one reason why I much prefer to connect to the tablet using wi-fi: with scp/sftp and ssh you can access all of the filesystem without worrying that half of it is about to disappear.