do you need...

No and maybe

Vista not needed at all. The games will probably be available for sale separately on steam only, but sometime after the Orange Box come sout.

Besides, if you haven't played the Half-Life series, then you have a serious problem...

No offense, but if HL is way to gory for your parents to allow you to play then how have you played it, and why are you asking about aquiring what's in the orange box?

To answer your question, NO Vista is NOT required, and YES you will be able to purchase everything that comes in the Orange Box individually through Steam.

ive played the half life series but its WAY to gory and my mom wont let me play itstevemcguy