Help converting Z axis of vertical mill

Hi,

I have been lurking on this group for a while now reading up all I
could on converting machines to CNC.

I have taken the plunge and decided on EMC to convert my vertical
mill. I have purchased ball screws (HIWIN) and fitted them to the X
and Y slides.

I cannot make up my mind on how I should tackle the Z axis of my
mill. I have put together a web page to outline the problem

http://www.geocities.com/kiran_list_groups/index.html?1037541612725

I will be really glad of any help you guys can give me.

Thanks

Kiran