Relax man, You didn't brick Your device, take it easy.

Marshall wrote fast and easy "tutorial" on how to make Drop Box working on N900 now - it's all correct now (well but it's still up to You where You saved files to untar). So install DropN900 again, read instructions, enter commands, authenticate new app (I presume that You didn't get there yet), and enjoy it. When entering new command will give You an error, check it and do it again, remember to check paths to files You saved - you just placing files in folders with by untaring them to spec. location - so there is no reason to be worried.

For futher, I can advice You to install BackUp Menu - very handy, but still You have to use it with care.

Good luck.