[Freetype] some questions about freetype

[yandongyao]

I have several questions when I use freetype:
1) I use freetype get the units_per_EM of simsun.ttc(copy from windows
xp),and units_per_EM=256, but on windows xp, I use fontlab 4.6(demo) get
the units_per_EM of simsun.ttc, and its value is 1024. why?
I think that units_per_EM comes from head talbe's unitsPerEm, so its
value shouldn't  different.
2) I want to display text vertically, and I need get column's width, but
how to do when using freetype? what is the meanding of vhea table's
ascent and  descent, could they be used to calculate the column's width?
3) I care about the vertical layout, and want to display large amount
text vertically, I have read some source code of freetype ,but I found
freetype hasn't consider vertical layout enough,could you give me some
hints?

thank you for very much! Any suggestions are welcome!!!