Use Years, banking, and borrowing can be confusing at times, especially for new members. I always like to suggest you make yourself a use year chart for your contract. In your case it's a March UY Chart and looks like this:
<b>Use Year.....Vacation Dates</b>
2004.....Mar 1, 2004 through Feb 28, 2005
2005.....Mar 1, 2005 through Feb 28, 2006
2006.....Mar 1, 2006 through Feb 28, 2007
2007.....Mar 1, 2007 through Feb 29, 2008
2008.....Mar 1, 2008 through Feb 28, 2009
and so on.
The points that are used for a vacation are determined by the vacation dates. For your May 2005 dates, points must come from your 2005 UY. You can get points into your 2005 UY three ways:
(1) Your regular annual allocation which you will receive Mar 1, 2005
(2) Banked points from 2004
(3) Borrowed points from 2006
Since you apparently won't have enough points in your 2005 UY to make your reservation (either banked 2004 points if any, and your new 2005 allocation (minus any that were previously borrowed), MS will automatically borrow as many points needed from your 2006 UY. They will explain to you that once borrowed they cannot be returned to 2006.
As for actually making the reservation, it has nothing at all to do with your use year. You reserve at 11/7 months accordingly. The date you're reserving determines what use year the points must come from, and you simply bank, borrow, or use that years regular allocation points as necessary.
In your case, assuming it's your home resort, you could have made your May 2005 reservation as early as last June, 2004. Even though you would be calling them in 2004, they would still have used points from your 2005 use year since May 2005 is in that UY, and would have borrowed 2006 points as required.
Hope this helps.