Wanting a fresh reinstall

I'll get right to the point and try to be as specific as I can. I have installed Windows 7 home premium on my XPS laptop. I previously was running Vista home premium. When i start my machine, it asks me if i want to start with vista or 7.

The trouble is that when I select 7, it boots up and still has all my previous vista files on my partritioned hard drives. This is a problem because both were badly infected by viruses. I want to COMPLETELY delete ALL files and do a clean install of Windows 7 so that W7 is the only OS on my computer. Hitting f12 as my computer starts and asking it to boot from the W7 disc only results now in the machine booting up normally. How can I just delete everything and start anew?

When you installed Windows 7 Did you select the correct Hard Drive and while installing it should have asked you for an Upgrade or Custom install (Clean Install)

Warning: This will completely wipe clean your entire Hard Drive and no files will be saved! This "Clean All" command is to zero your drive which is the deepest possible clean against infection. The following commands will format and mark active the drive, preparing it for immediate Win7 install.

Boot from the Windows 7 DVD and on the second screen select "Repair my Computer," then in the Recovery tools list, select Command Line and type:

DISKPART
LIST DISK
SELECT DISK # (for Windows 7 disk)
clean all
create partition primary
select partition 1
assign letter=c:
active
format
exit

Now boot back into the Win7 DVD and select Custom install, select the drive you just cleaned and formatted, and install Win7.

Problem with 'clean all' is that it can take the best part of a day to do it's job! Clean is a lot quicker but not as thorough.