Problem with date range lookups and calculations

I have a date calculation problem, which I hope someone can help me with.

I have a spreadsheet as follows: (this is a simplified example)

……...…A……...………….B………………..C
01…..….date…………..salary….….rolling average
02….30-01-08………..£2000………….£24,000
03….28-02-08………..£2000………….£24,000
04….31-03-08………..£2300………….£25,200
05….29-04-08………..£2300………….£25,800
06….30-06-08………..£2400………………?
etc
etc
etc

I am trying to calculate my rolling average yearly potential salary (ie “how much would I have earned in the last twelve months if I was paid at my current rate for all those preceding months”?), based on amounts entered throughout the year, usually monthly. However, there can be more, or less, than 12 salary payments in a year, as sometimes I am paid weekly and sometimes not at all for a month. (I work as a musician on cruise ships, and I work short contracts ie 3 months on, 1 month off, three months on, 1 month off, etc. All salaries are paid at month end and amounts can be different from month to month. Prior to this employment, I was paid weekly.)

In the above simplified example, the calculation for C2 is easy, as I just take the monthly payment B2, multiply by 12 and there it is.

Also easy is row 04 – I add B2+B3+B4, divide by 3 to get a monthly average and then multiply by 12.

By row 05, we can see that my rolling average is increasing as my salary has increased, which is the figure I want to calculate. However, row 06 shows there was no payment in May, and I negotiated a new contract rate in June, so the calculation I want is much harder. I have to now work out a DAILY RATE, by looking at all earnings in the last 365 days, adding them, dividing by the number of days (there will be less than 365 for at least the first 12 entries) and then multiplying by 365 for the answer. In my example, this would be as follows:

£11,000 (total earned) / 153 (days between 30-01-08 and 30-06-08) = £71.89
£71.89 x 365 = £26,241.83

showing that my rolling average increased, which is good news!

I therefore need a formula that will look at all dates in column A, select those that are within a year of the most recent entry, calculate a daily rate using the amounts in column B and put the result in column C. I have found the function EDATE which I guess is the one to use (as the operator ‘-12’ will return the date exactly a year earlier), but I’m unclear how to use this for what I want. I think I need to create an array, but how do I specify parameters for the highest and lowest dates in that array? Or perhaps this might have to be done using pivot tables/calculated fields/calculated items/etc, but that is a very alien area to me and I’m totally unsure where to start if such is the case.

If anyone can offer any assistance or suggestions, then I would be most grateful.

Many Thanks