What you are looking for is the Future Value (FV) formula, as applied to a fixed present value and an annual annuity.

http://en.wikipedia.org/wiki/Future_valueSo first off the future value of your 150k in 5 years with 4% real returns is 150k * 1.04^5 = $182497.94. So what you need to save from your annual payments is 617502.06.

The formula for the annuity is listed near the bottom of that wikipedia page. Solve for payment amount:

PmntAmt = (FV*r)/([1+r]^n - 1) where r is the rate of return and n is the number of compounding periods.

To plug in your numbers:

FV = 617502.06

n = 5 (assuming annual compounding)

r = 0.04 (7% nominal returns - 3% inflation)

Payment Amount = 114007.62

So, as you can see, over a short 5 year time period the compound interest doesn't give you a huge boost. If you rework the numbers for 10 years it looks like this:

FV(150k) = 150k*(1.04^10) = 222036.64

FV(required from payments) = 577963.36

PmntAmt = $48139.11