I've written about women at war previously; as I've said before, I don't think there are any good reasons for allowing women to serve in combat positions, and there are plenty of very compelling reasons not to.
I came across a post on a site called Equity Feminism that notes that when women recruits are held to the same physical requirements as men are, their injury rate increases by more than 100%.
Great Britain used to train men and women separately, with different requirements, but many women soldiers finished basic training without the abilities needed to perform their jobs. In 1998, the army began holding women to the same standards as men, and this change in policy resulted in the discharge rate due to training injury for women to rise from 4.5% to 11%, a jump of almost 150%. [Update: medical discharges for men were below 1.5%, according to the source BBC article.]
Regardless of anyone's opinions on the matter, women simply cannot attain and maintain the same physical abilities than men can, and as such they make inferior combatants. As I've written, in some circumstances (such as in Israel) every fighter is necessary -- perhaps because the population is small, or the war is particularly large. America is not in such a situation, and we have the luxury of keeping women out of combat roles in our armed forces. This policy improves the quality of our military in numerous ways (as I've outlined in my previous postings), and also serves a valuable social function.