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)