It all depends on how you backed up and restored your Outlook data.
Do you still have access to your original pst-file from before the
reinstallation?
Copy that one over to your new machine and then reconnect it in Outlook via;
File-> Open-> Outlook Data File...
If you did an Export/Import in order to bring over your data, could it be
that you skipped a few folders in that process?
For more information about how to properly back up and restore your Outlook
data see;
http://www.howto-outlook.com/howto/backupandrestore.htm