How do i reinstall my OS?

One of my friend has these problem last weekend as he had a mess with his Windows Vista Operating System.

Here is what he quoted down in his mail..

I am running Windows Vista 32 Bit, it came on my computer. the computer DID NOT come with the Windows Vista disks, and as far as i know i do not have a registration key for vista. i got this b.exe trojan and thought i fixed it but ive been having internet speed issues ever since, and every time i run a trend micro scan (even in safe mode) it gets stuck on this certain file. ive ran malwarebytes and it found and removed some things, as well as spybot Search and destroy AND Hitman pro. i just cant seem to get rid of these stupid trojans and im considering re-installing my OS. will i be able to do it without the disks? and can i find what the registration key for my vista is off of my pc some how? and is there a step-by-step guide i can follow to reinstall it if i am even able to? ive never installed or Uninstalled an OS before. but im starting to feel this is my only option to rid myself of these trojans.

I just wanted to post these so that any one who encounters such a situation can get the fix right here for his Vista Installation Support at his perusal.


Step 1
Review the system requirements for Windows Vista 32 bit. For Windows Vista Home Premium, Windows Vista Business, Windows Vista Enterprise and Windows Vista Ultimate versions, the computer must have at least 1 GB of RAM and a 1 GHz processor. Vista Basic requires an 800 MHz processor and 512 MB of RAM. All versions also need a 32-bit or 64-bit processor available.

Step 2
Insert the Windows Vista 32-bit installation disc into your computer's CD/DVD drive. Open the "Start" menu and select "Run" from the available options.

Step 3
Type "Drive:\setup.exe" into the "Run" window once it pops up on screen. When the Windows Vista 32-bit installation wizard appears, you can select "Install Now." To continue, choose the "Custom" install from the installation menu if this is a clean installation. If you are upgrading from an older version of Windows, then choose "Upgrade."

Step 4
Follow the on-screen instructions to allow Windows Vista 32-bit on your computer. You need to agree to the terms, as well as enter your product key to activate the operating system. Once the installation is complete, the computer will restart with the new OS ready for use.