Excel IF Nested Formula

I use Excel 2003 (Win) and need help with an IF formula. I will try to describe what I need.

If cell E7=8550 or 4586, I want the result to be a 3.
if cell E7=8510 or 8520 or 8521 or 8574 or etc, I want the result to be 1.
if neither of the criteria is met, I want the cell with the formula to be blank.

Can you help me? Thanks.

Juan

Thank you sooooooo much.
Juan