New windows 7 computer?

hey guys, i just got a new windows 7 computer and its like fully new, i don't know if it has direct x in already and i want to play my old games like far cry 1 and quake 4, quake 4 comes with direct X9c after when u install quake 4 it asks u if u want to install direct x9c, should i click yes? what if i have direct x10 or something like that and i installed a lower directx, what will happen, please help me out here.