Nero 8 installation

Hi pals,I downloaded nero 8 ultraedition recently.The file is around 183mb.But installation is a problem.During a prolonged procedure the installation stops at a point when it asks needed DIRECT X 9c.I check my system it has only 9b.I know microsoft wont provide this update unless i go through WGA.
I have few questions
1 How to install Direct X 9c
2 What is the advantage of nero 8 in burning dvds over nero 6
3 If i am having nero 6 do i need to upgrade really if I want burn downloaded movies in different formats to dvds

I am a healthcare professional.My desktop has P 2.4GHZ processor,750 MB ram,160gb hard disc,DVD RW drive.:confused:

1: Buy a legal copy of Windows XP
2: Almost nothing. 8 can deal more formats and models
3: if you want to convert them and use Nero for that it can be beneficial