Your UY is simply the time that your points become "active". It in no way affects when you book. Regardless of your UY, you can always book 11 months out for vacations--in your case, you will always be able to book in March for Feb vacations.
Typically, having a UY that falls right before you travel can be a good thing as it allows flexibility in what you can do with the points if you have to borrow points for the trip, or change/cancel your trip (at least 31 days out--if you cancel/change the trip with less than that, something different happens to the points).
You can "bank" your points within the first 8 months of your UY. So for Feb vacations, you would want a UY that happens in the fall. Dec UY would be the best (gives you until July 31st to bank), but Aug/Sept/Oct would also work out.
When you call to book a reservation, MS looks to see what points you will have available at the time you travel (not when you book). To pay for a trip, you can use "banked" points from the previous UY, current UY points, and borrowed UY points.
For example, say you had a Dec UY for 150 points. You want to travel in Feb, 2011 and use 400 points.
Since this trip would fall in your Dec 2010 UY (which runs from Dec 1, 2010 - Nov 30, 2011), you could pay for it by "banking" the 150 points from Dec UY 09 into Dec UY 2010, 150 2010 UY points, and then borrowing from 100 points from your Dec 2011 UY.