Step-by-step guide to formatting HD and reinstalling OS

I have some troublesome malware with root kit.
I am preparing myself for needing to format the hard drive and reinstalling the OS.

Could anyone direct me to a good step-by-step guide to doing this?

As an aside, I have Windows Vista, which I got legitimately, but no longer have the disks. So I would have to buy new disks for Vista before I could reinstall. If I am buying an OS would I be better off buying Windows 7 and installing that instead? (I am familiar with both, though far from expert, and slightly prefer using W7)

Some hardware details in case they are relevant:
It is a Packard Bell IMEDIA X2416
Intel Core 2 Quad CPU Q8200 @2.33GHz 2.34GHz
4.00GB Ram
32 bit OS

 

Get |MG| Parted Magic

This link will take you to Major Geeks page where you can read about it and download the .iso file. You will need to use a program such as |MG| ImageBurn to make a bootable CD of Parted Magic.

You boot the computer to this CD and follow the guide at Parted Magic's site

Things to do first:

• Backup your files to removable media, i.e. CD/DVD/USB stick.
• Have a licensed Operating System Disk ready to go to install.

I'm not sure if you can even find Vista for sale, Windows 7 would be my choice. Amazon.com may be your best bet for buying 7 at this point.

 

If you should decide to stay with Vista, ebay has Windows Vista in various configurations.