Windows 7 how to Format win 7?

Read this page, (especially step 3) it will tell you everything you need to know.

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Are you trying to format in order to get rid of Windows.old? You can delete it if you boot from the Windows DVD.

The first time I installed Win 7 (it was the beta) I did the same thing. I was able to just delete the windows.old file.
It was a huge file and there isn't any option during install not to create the file.

Deleting the file still leaves remenants of the XP install in the root of C:\.

It's better (less messy) to format first.

Of course if you format a partition you will lose everthing on that partition so if you have any data you don't want to lose, back it up.

I restored my XP install using an image I had prepared beforehand and created a 22 GB NTFS partition at the end of my drive and installed Win 7 to that empty partition. I used that partition to do a clean of Win 7 RC but I made sure to format it from my XP install first. I did have to use Partition Magic 8 in XP to format though because the DiskManagement tool in Windows refused to perform the format with the message that the partition in question was in use.

Probably could have performed the format from XP safe mode but I have Partition Magic so I used that.