Hello Marc & All,

 I live in Central Massachusetts and have several hives that are low of food
 stores.

Hives low on stores need to be fed.  Not knowing the particulars of your
situation makes advice kind of general.  Weather is a big problem with
winter feeding.  The safest way to feed is to use a frame of sealed honey
out of one of your other hives.  Second is to make candy.  Recipes are in
the archives and bee books.  Like making fudge.  Place the *candy* directly
over the cluster.

> Can I start to feed syrup at this point?

You can if the weather is warm enough for the bees to break cluster.  What
happens many times with early feeding is the bees break cluster and go to
the feeder in the day.  Then the temperature drops rapidly and they don't
make it back to the cluster.  Wraping hives helps with rapid drops in
temperature.  If the temperature in your area has been warm enough for the
bees to fly and move around the hive then in a few hours they should pack
the syrup into the cluster.

 Should I use 2-1 or 1-1 ratio of
 sugar to water?

Most beekeepers (myself included) use the lighter mix for spring feeding.

 Will this stimulate the bees to overpopulate too early?

Depends on the amount you feed.  I doubt a gallon now would be a big
problem.  Pollen is more of a stimulant than syrup.   These answers are
fairly general.  I could maybe give better advice with exact situation
details.  Hope I have helped.
Sincerely,
Bob Harrison
Odessa, Missouri