I am so sorry that the terminology I used confused you. You're correct that you are only paying tax on the interest and profit. When I mentioned the partnership should know when you were paid, or when I mentioned that US is on a cash basis, the money I was always referring to was the interest and the profit. THAT is what is taxable to you.
Most companies pay interest either quarterly
or yearly, and your % of the profit was probably paid either quarterly or yearly. The interest and the profit earnings were what I was referring to when I mentioned checking with the partnership to see when the payments were made.
An alternate way to figure interest, if it is earned by the partnership ratably, is to divide the $ amount earned by 12 months, and then use the portion that would have been earned in 2009 calendar year.
In a pinch, you may do the same for the profits, but its always better/cleaner to get the exact dates that the interest and profits were paid to you if they're available.
Please let me know if you have follow up questions, and I will try to remember how much terminology can muddy the waters, especially when it comes to people's finances.