being a woman of islam, ill answer q's 2,3 and 4.
i am not sure about q1.

2) Why is a woman's testimony only worth half a
man's?

this is true because women tend to work more from
emotions. they have a softer heart and relent to
temptation faster.

3) How come Islam allows men to beat their wives?

Islam doesnt allow men to beat wives just for
fun. a man can not hit me unless ive gone against
the path of Allah or adultery. Even then he can
not hit me right away. there are steps leading
upto it. first he tells me its wrong. then he
separates his bed. and if even then i dont
listen, he can hit me with a miswak (wooden stick
used to cleanse teeth) no longer than his thumb.

this intends to attain two things...
1) if the woman has any haya in her, she'd stop
by the time the man separates the bed. if not,
she really s evil.

2) the length of the miswak... the length of a
thumb... it can never hurt u. the intention is to
reprimand not to injure.

also remember to judge a religion by its
scripture not its people. what muslims do today
is not what they are taught... just as christians
or jews or believers of any other faith. just
becoz a person does something doesnt mean the
whole faith does it.

q4... the lashing... and stoning... im still not
sure about this and i know there are conditions
that apply. i had it in a book which i cant place
right now.

however... even if the conditions are same...
lets remember that a woman is built less inclined
towards sex than man. it is tougher for her to
succumb to temptation. also, by her indulging in
fornication, she puts her lineage into threat.
especially if she's maried and i think stoning is
for married women only. it is also a way for men
and woen to be punished in this world rather than
facing it in the hereafter... which would be a
tougher and more brutal punishment.

salamoalaikum... all errs are mine and mine
alone... Allah is free of All errs.