Yes you need a DVD or flash stick installer both for the cleanest install and for later repairs if Win7 fails to boot.
Burn the ISO to DVD using ImgBurn at 4x speed with Verify - it never fails. You can get a 3 pack of Maxell DVD's at Walgreens for $2.
If you have been infected you should use DISKPART from the booted installer to deep clean your HD, otherwise boot the DVD, select Custom install, use Drive Options to delete all partitions , create New one(s) as you wish, then format before installing Win7 to first parttition.
Be sure to back up your files and make your Vista recovery disks from the Recovery partition as it will be disabled during install and can be deleted to recover the HD space.
The installer is nearly driver-complete with newer drivers arriving quickly via optional Windows Updates. Any drivers then missing in Device manager can be found on the Suppport Downloads webpage for your model computer or device. Don't change out any drivers given by installer unless performance or video requires it.
Install programs slowly so you can gauge performance after each. Don't let programs write themselves into your Startup list at msconfig as they become freeloaders on your RAM and CPU when not running. I only allow my AV and gadgets in Startup and have 30 second startup/shutdown and instant performance.
After you have it configured as you want, clean and order the HD using freecstate-of-the-art CCleaner "Run Cleaner" and Registry tab, then Auslogics Disk and Registry defraggers, then save a Win7 backup image externally so you never have to reinstall again - just reimage the HD or a replacement using your DVD or repair CD and the saved image.
