Other contributors have said "When does a vermal equinox occur?" is the same question as "When does a vernal equinox occur?". If you believe that these are not asking the same thing and should be answered differently, click here.
In March; for 2009 it's the 20th at exactly 11:44 AM.
The word vernal is derived from the Greek word for spring, but because it only occurs in spring if you live in the northern hemisphere, it is now properly revered to as simply the March Equinox