Hi Kerjuk – unfortunately you will need to restore this public store to a machine running same version and service pack as it came from … i.e., Exchange 2003 with whatever service packs you were running at the time. Once you get the public folders back you will want to replicate them over to your Exchange 2007 environment, and then decommission the Exchange 2003 public folder replicas once you’re sure you have everything you need.
There are some third party solutons available on the market that simplify this, but that’s at an additional cost, so depends how important those public folders are to you. Google “public folder recovery backup” or similar to find them.
Hope that helps!