Hello Cindy,
What you can do is Export the Invoice Data from CRM 4.0 into a CSV file. From here you can import the data as an Invoice in CRM 2011 by selecting the following options.
1. Click Imports in the Left Navigation Pane
2. In the ribbon click Import Data
3. Browse to the location of your CSV file and select it
4. On the delimiter Screen, change the field/data delimiter if needed, otherwise click next
5. On the Select Mapping Screen choose > SampleDataMap
6. On the next screen under "Microsoft Dynamics CRM Record Types" Select Invoice
7. Finally Mapp your respective Fields in the CSV file to the CRM Invoice fields and import the data.
Best Regards,
Brian Storie
CRM Support Engineer