women's crit racing?!

There may be some Juniors racing, or Women's Cat 4...I don't know how active bicycle racing is around you.  I won't give you any advice on crit racing, because I'm not particularly good at it.  No real special gear beyond a road bike...but if you're doing group races I'll assume you already have one.  You can get a one day license at the race, or buy a USAC license for $60.  I'd only go that direction if you're going to do more than 6 races this year, and by this year I mean before December 31.

There may be some Juniors racing, or Women's Cat 4...I don't know how active bicycle racing is around you.  I won't give you any advice on crit racing, because I'm not particularly good at it.  No real special gear beyond a road bike...but if you're doing group races I'll assume you already have one.  You can get a one day license at the race, or buy a USAC license for $60.  I'd only go that direction if you're going to do more than 6 races this year, and by this year I mean before December 31.

Hopefully JenG and/or dredwards will post here, both very fast women (in the good bike way)

X2, 
Have you considered a coach Alice, it would be a great source for direction and technique,tactics and information on training. I race Cat5 mens and know the dynamics of womens racing is so much different so I cant help as well, but will say you can tell at races the difference between coached and self coached.
USA Cycling has much information about racing and team and race info on thier website. Getting on a team is another option that will get you ready for racing, check out some local races and try to get to know some of the racers,promoters,coaches for information.

Hi Alice, I sent a "back channel" response, but realized I didn't answer all of your questions.

You do need a license. I'd recommend getting a full year license and planning on doing a few races. The first will not give you a sense of what you can do necessarily, as it is such a unique experience that it takes some learning.   Other than the license, you don't need anything special in terms of equipment or gear.  If you aren't on a registered USAC team, any plain jersey with sleeves is proper.  Any road bike will do. It does not have to be fancy.

Intervals will help with fitness, but there are riding skills involved in criterium racing that are essential and really can't be learned on your own.  It's very important to get the experience in fast groups so that you can be relaxed and safe with close riding, cornering, and even possible contact with other races.  However, ultimately, you have to race in order to get better at racing. 

As far as speeds, the averages would probably be somewhere between 21mph and 24mph for a women's cat3/4 race, depending on the course, conditions, and size of the field (the lower end would be for a hilly course and small field).  The average speed is usually not what cracks people in criteriums, but the repeated intense surges at very high intensities.  While it may seem logical that you could just get out on a break if you can TT faster than the group is riding, it doesn't necessarily work that way.  The strongest riders in the pack are not riding as fast as they can most of the time. When the pack is going slow, they have lots of energy in reserve to attack, chase down breaks, and sprint.