You don’t have to erase nor reformat anything, that would be a loss of time - it’s not even the same filesystem, XP uses NTFS and OS uses ext3 (by default, you can choose another FS but not NTFS, I’d think).
The installer will propose to create a new partitioning scheme, erasing whatever it has to erase to create (and format) new root and swap partitions, and a separate /home partition if you want.