If you copied the entire folder at Start-->My Document-->Electronic Arts-->The Sims 3 -- just start your game to generate an empty save file. Move it to a safe location as a back up and copy the saved files you transferred to the USB in its place.
I would of suggested that you copy everything in these folders,
Screenshots All of which is located under C:\Documents and Settings\Corey\My Documents\Electronic Arts\The Sims 3 assuming you have Windows.
Then simply re-install The Sims 3 on your new computer or wherever you wish to put it and re-paste all of those folders back to where they originally were. If you have any saved worlds, patterns, or even hacks located in the C drive than you need to keep in mind that you have to copy those to.