Direct x 10 for bootcamp booted vista?

right now i have a macbook and i have downloaded bootcamp and got window home premium. i am waiting for games like halo 2 and quake wars to come out for vista. can my macbook play those games??? So what i am asking when i downloaded the home premium the direct x 10 was also downloaded if not where can i download direct x 10. Finally i got a 160gb external harddrive since i am running low on memory can i download games like halo 2 and quake wars on the external harddrive only and if i do can i play it in my laptop??? thank you for answering the questions xP