Before you use Outlook Mail Recovery, make sure you make a backup of the damaged pst file. When you have scanned and repaired your Outlook 2003 PST, you should have no problem using it with Outlook 2007.
Also, make sure you are using the right kind of scan for your particular damage. For most damaged pst issues, you can use the Normal Scan feature in Outlook Mail Recovery. If the PST file is too damaged, you can use Smart Scan, but be aware, it takes longer.