It is good idea to use sync software. Also you can use the pst recovery or Outook extraction software. For example: Outlook Export Wizard allows to extract emails, calendar, contacts etc. It saves Outlook items as files of appropriate formats (emails as MSG or EML, calendar as VCF (virtual card file)). But it also able to save all data as MSG files, so you can just drag MSG files extracted from Outlook 2010 and drop them to the Outlook 2007 folder. With Outlook Recovery Wizard you can just proceed the recovery and it should save the PST file in compatible format.
I used the export wizard for the same task, that was fast and convenient.