Yep, I concur with the previous poster. The most accurate information available is your reported income on each year's W-2, and if there's any discrepancy in a future background search (if your company did something like multiply hourly salary * 40 * 52 to calculate it or similar) it's very easy to support the number you provided.
To estimate this year's annual income, I am assuming you don't have ready access to your total number of hours worked each year or you would be defaulting to that. So I would take FY2009 total salary * the percentage of FY2010 you received that same salary, + FY2009 salary * raise % * the percentage of FY2010 you receive the new salary. As that isn't easy to follow in words, let's use numbers to illustrate:
FY2009 hourly salary: $20/hour
FY2010 hourly salary: $25/hour (for a 25% raise)
Total FY2009 compensation: $50,000
We'll say your raise was effective May 1st, so 1/3 of the year was at your old salary, 2/3 of the year at your new.
Your estimate would look like this:
$50,000 * 1/3 = $16,667
$50,000 * 1.25 * 2/3 = $41,667
$16,667 + $41,667 = $58,334 estimated FY2010 salary
This essentially relies on your working about the same amount of overtime as you did last year, but it should be the simplest calculation without needing to ask for an HR report or needing to get specific as to calculating time & a half for your overtime hours.
Hope that helps!