Deleting and formatting are not the same. A partition is simply a portion of your HDD. Suppose you have a 120 GB HDD you could divide it into several virtual disks which would be called C: D: etc... these are your partitions.
During install, XP will ask you if you wish to delete a partition. By selecting YES, you remove one of those virtual disks.
When installing, it asks you if you wish to format using either FAT32 or NTFS, quick or normal format.
If you select to create more than one partition and fail to format the ones where windows will not be installed, you won't be able to use this partition until it is formatted. This can also be done in Windows
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