Summarising from across forms

Hi,

I'm just wondering how to go about summarising data from across different forms.

If, as an example, I had a form recording sales and I had another form recording expenses, would I be able to summarise that data on another form to show sales, costs and profit totals for a specified period on another form?

In a related question, as far as I can see a report can only work on a single form type at a time. Is that correct?

Cheers

Matty