I just blew away my edits by mistake. Here is what I think I had...
You might want to combine project and invoice tables.
[Person](Id,FirstName,LastName)
[Company](Id,Name)
[Consultant](Id,CompanyId,PersonId,HourlyRate)
[Owner](Id,PersonId)
[Approver](Id,PersonId)
[Invoice](Id,Description,Capital,CompanyId,OwnerId,ApproverId,AssignedOn,DueOn,CompletedOn,ReceivedPaymentOn)
[Activity](Id,Description,EstimatedHours)
[InvoiceLine](Id,InvoiceId,ActivityId,ConsultantId,ActualHours,AssignedOn,CompletedOn)
[BillingPeriod](Id,Description,StartsOn,EndsOn)
