Unfortunately, rules are not stored in the .PST file. Rules have to be exported separately. If you can access the old image, you'll want to open Outlook 2007 and export the rules so you can bring them over.

Open the Rules and Alerts window (Tools > Rules and Alerts), and click on Options, there will be buttons to Export and Import rules. The rules would be exported into a .RWZ file, which could then be imported into Outlook 2010.

-SW